West Midlands Police said it had received a report of malicious communications after Carl Benjamin, who is standing for the right-wing party in in the South West region, discussing sexually assaulting the politician on YouTube and Twitter.
Mr Benjamin, a vlogger who goes by the name Sargon of Akkad online, tweeted Ms Phillips in 2016 after she discussed rape and death threats sent to women on the internet.
“I wouldn’t even rape you, @jessphillips” he wrote. He has since been banned from Twitter.
Mr Benjamin doubled down on the comment after being selected as a Ukip candidate for this month’s election, defending the “joke” and refusing to “apologise for my crimes against political correctness”.
In a video posted on YouTube late last month, he said: “There’s been an awful lot of talk about whether I would or wouldn’t rape Jess Phillips. I’ve been in a lot of trouble for my hardline stance of not even raping her.
“I suppose with enough pressure I might cave. But let’s be honest nobody’s got that much beer.”
A police spokesman said: “Police have received a report of malicious communications relating to MP Jess Phillips.
“Officers have spoken to Ms Phillips and the comments are being investigated to establish if an offence has taken place.”
Ms Phillips told the BBC’s Victoria Derbyshire on Tuesday she broke down in tears in Birmingham city centre after learning of Mr Benjamin’s latest rape comments.
The Labour MP, who is frequently targeted by online trolls, said: “I realised that I did what all women do in these situations – I had been putting a brave face on it and pretending that it was all fine and that I could cope.
“It sort of dawned on me that, for four years essentially, this man had made a career out of harassing me. And I felt harassed. I felt, ‘How can somebody say that they would rape me if forced, and be a legitimate candidate in an election?’
“It was one thing when he was just some idiot off the internet with a load of bros following him. It is a different thing when he is standing on the same platforms that I am standing on, that he will potentially go to a parliament himself as an elected representative when he has said these things.
“I just cannot believe our system is so weak at the moment that that’s allowed to happen.”
She added: “I cried in the street in Birmingham city centre, just because I felt the enormous weight of years and years and years of abuse.”
Mr Benjamin, 39, from Swindon, was investigated by Wiltshire Police after his initial 2016 tweet to Ms Phillips was reported to the force in December last year.
A spokeswoman told The Independent he was “dealt with by words of advice”.
Wiltshire Police is also looking at a file of information, understood to include multiple social media posts, which was handed to officers last month.
The force said the dossier was “being reviewed” but its inquiry was “at an early stage” and no formal investigation had been launched.
Mr Benjamin has not been arrested by either West Midlands or Wiltshire police.
Ukip did not immediately respond to a request for comment.
The party’s leader, Gerard Batten, has previously defended Mr Benjamin’s 2016 rape comment, which he claimed was “satire”.
Last month he stormed out of a Sky News interview after growing angry about being asked about the tweet.