He is in no doubt as to the cause of the disaster. "It's that bastard there," he says, pointing past the original Severn bridge to the second crossing, five miles downstream. He claims that the accretion of mud began soon after construction of the new bridge started, in 1992. Before that, he used to walk out a mile to fish over rock scoured bare by the tide; now the glutinous sludge is 9ft deep, and would swallow any man trying to cross it.
What has happened - in Philip's view - is that the 40-odd caissons supporting the second bridge have taken the force out of the tides, which rise and fall as much as 40ft and are among the most powerful in the world. The result is that silt is no longer carried past in suspension, but falls out of the slacker water and builds up on the bottom. He is now seeking compensation for the loss of his livelihood from the Department of Transport. The powers-that-be disclaim responsibility, and maintain that the silting of the lake and the approaches to it has been caused by natural shifts in the bed of the river.
Philip is the last of a long line. His grandfather, father and uncle all spent their lives fishing the river, and he himself grew up with no other ambition than to follow in their footsteps.
For centuries salmon have been caught off Oldbury in two forms of trap: putchers - tapering, conical willow baskets set out in tiers across likely stretches of the river - and lave-nets, which resemble giant shrimping nets and are manipulated by individuals standing in the water. Both devices depend on the fact that in the lower reaches of the Severn salmon cannot see, because the water is opaque, full of silt stirred up by the tremendous pull of the tides.
In recent years putcher fishing has declined, with a drop in the numbers of salmon coming up-river. But lave-fishing continued to flourish until recently, especially off Oldbury, in a long, narrow pool a mile out to sea, left behind by every falling tide.
For a stranger, it is fascinating to look out across the glistening, three-mile expanse of the estuary and watch the tide go down. On a cloudy morning everything is a mysterious gunmetal colour - water, sand, mud, sky, all grey - and it needs an expert such as Philip Jones to interpret the changes that steal over the scene.
"See that horseshoe mark coming up?" he says. "That's where the pool is. He'll be up in a moment. See those two pieces of rock starting to show? That's what I call the Haddock. Only they aren't rocks; they're man-made walls, built to keep the fish in."
In the old days Philip would walk out with his lave-net and take up station on one of the Standings - three-tiered stone platforms built for the purpose. The pool, he explains, used to be about 6ft deep for much of its length; fish cut off in it by the ebbing tide would drop back towards the seaward end.
There, finding themselves above a rock shelf, they would turn back upstream, and the lone fisherman, spotting a fin or a track through the water, would lower his net as it came towards him.
Fresh-run fish were prized in local pubs - the Anchor at Oldbury, the Windbound, the Berkeley Arms - and Harvey's restaurant in Bristol prided itself on serving the first Severn salmon of the season.
Now the tradition of Oldbury fishing is gone, buried beneath 25 million tons of blue-grey sludge.