Next week she opens in Sondheim's A Little Night Music, dizzyingly staged by Sean Mathias on the Olivier's revolve. She plays Judi Dench's mother (that's the magic of theatre for you), the worldly Madame Armfeldt, confined to a wheelchair and freely dispensing wittily astringent advice: "To lose a lover or even a husband or two during the course of one's life can be vexing. But to lose one's teeth is a catastrophe. Bear that in mind, child, as you chomp so recklessly into that ginger snap" (a sentiment wholly shared by this elegant and most beautifully preserved 60-something actress). The part includes the song, "Liaisons", a potential showstopper, but one with all the length, complexity and pitfalls of a Shakespearian soliloquy. "You do feel you've come to 'To be or not to be' and that all the Sondheim buffs are waiting to see what you're going to do with it."
Not that she is daunted. She sings well (her father was a leading chorister in the Welsh valleys) and thinks positively. "With a couple of wigs and a bit of acting, I think we'll manage." Her fine bones and expertly painted face, outlined by the shortest, sleekest, flattest of haircuts, may suggest a porcelain brittleness but, according to Sean Mathias, she's a tough cookie. "She looks delicate, then you see her tuck into a crate of bacon and eggs and steamed pudding in the National Theatre canteen - just like a truck driver. And she's so stubborn that you have to treat her like a truck driver. She goes off from rehearsals and cooks up her part and comes in the next day and wants everyone to do this and do that - I've never known anyone so manipulative. We have terrible fights. She has an outer skin which is like an oriental mask and an inner sensibility which is Welsh farming stock - pragmatic, tenacious and game. It's what makes her such an interesting actress."
Her childhood explains something of this. It was How Green Was My Valley but in shorter frocks, as tough as it could be in the Thirties in south- west Wales. Tough, but cultured. "I'm the last of the highly educated peasants," declares Phillips. A sickly child, plagued with diptheria and scarlet fever, she had little conventional schooling until she was 10, so her mother, a school-teacher, encouraged her to memorise poetry. Phillips can still recite a dialogue in Old Welsh between an old man and his more cheerful self - a piece eloquently chocker with assonance, dissonance and alliteration - with which she won the National Eisteddfod at the age of 11. "Every child in our community was required to perform - dancing, singing, playing the piano. My mother was happy for me to enter myself for the eistedfodds because the festivals took place in chapel. When I tried to join the Brownies I might just as well have suggested joining the Hitler Youth, she was so scandalised by the waste of time learning to tie knots."
Her mother's instinct proved right. The BBC spotted the talented youngster and through grammar school (she got a scholarship) and university she earned a respectable living as a radio announcer and newsreader. Her parents wanted her to continue her career with the respectable BBC and refused to let their daughter go to Rada until she had completed her philosophy degree. "My parents weren't ever a bit impressed with me. When I began performing as a child I was always told, 'No one's looking at you' - they were always reminding me that I wasn't anything special - and of course I believed them. But it's a bit of a drawback as an actress."
After Rada, Phillips went on the rep trail. "Then I met O'Toole and fell madly in love." (It's impossible to divine whether her invariable omission of "Peter" indicates intimacy or hostility. She claims that she has "great admiration for his work"; they don't speak.) "I wanted to be a single career woman, but I also obviously felt some need for a home. I remember Sybil Thorndike and Flora Robson were all wheeled out to tell me marriage would ruin my career and I said it would be fine. But of course it wasn't. Girls build up a system of people - usually men - who like their work and promote and push and protect. They were all platonic relationships, but they were emotional - and husbands hate that. So I lost my supporters and O'Toole went off to the desert to become Lawrence and an international movie star."
She says she didn't complain, she simply complied. O'Toole said have children, so she had two ("I wasn't cut out for motherhood, but I was dutiful and punctilious as a wife and mother and I got a sort of kick out of doing it well); he said don't do Cleopatra at the Old Vic, so she didn't; he said she could work "as long as it didn't get in his way" and she felt that "all the shine had gone out of me. It was as if I didn't really want to do too well in case it caused a problem in my private life - I think tons of women have this to deal with."
Such is her poise and calm self-assurance now that it is hard to believe she was ever a pushover - and it is, of course, only her side of the story - but it does explain the considerable gaps in her cv. Phillips is up there with our most gifted actresses - Dench, Dorothy Tutin, Eileen Atkins, Prunella Scales, Eleanor Bron - but we've seen much less of her. She's done Hedda and a few Shaws, but no Chekhov and strikingly little Shakespeare. What she has done has occasionally been remarkable and memorable, particularly on screen - Livia in I Claudius, Lady Churchill in The Wilderness Years, Beth Morgan in How Green Was My Valley. She got two awards for Goodbye Mr Chips and the Gorsedd of Bards made her a druid of drama.
Phillips says it took her until her late thirties before she began to act in the way she wanted to. "The best was The Night of the Iguana at the Savoy when I was about 35 and Tennessee [Williams] was still around. We corresponded after that. He wrote some poems for me. It was so rewarding. For a time I felt part of a charmed circle." But her change of attitude meant the beginning of the end of her marriage to O'Toole. "I can't put my finger on a single incident - it was almost imperceptible - but the fact was that my career strained the seams of my marriage. My complete attention and commitment went elsewhere."
It would be quite wrong to say she has no regrets, she has plenty. "I'll never catch up - there's too much ground lost." But if there is bitterness, she won't admit to it and it certainly doesn't show. She's just returned from six months on Broadway in Stephen Daldry's production of An Inspector Calls, before which she spent a long time workshopping I Wish You Love, a vision of Marlene Dietrich written for her by Pam Gems and directed by Sean Mathias. "I've always been looking for this - something I can trot out when I'm not in work. It's like a pension." Her obsession with Dietrich goes beyond wise financial planning, however. It smacks of the wish fulfilment of a life of lovers and no laundry, total dedication to work without a flicker of guilt. "And why not?" smiles Miss Phillips. She's clearly working on it.
n 'A Little Night Music' opens Tuesday, Olivier Theatre, RNT, SEI (0171 928 2252)Reuse content