The Bridgerton actress began dating the King of Staten Island star in February this year, but it has now been claimed their romance has already started to fizzle out after busy work schedules have made it difficult for them to spend time together.
An insider said: "Pete and Phoebe's romance was a real whirlwind and from the start they were both totally committed. But as time has passed, it's become increasingly obvious it is going to be difficult to make this work.
"Phoebe has had back-to-back filming dates with Bridgerton in the UK. Meanwhile, Pete has been back in the US filming Saturday Night Live. Alongside that he has just started working on a new film, Meet Cute, with Kaley Cuoco."
The couple last saw each other in July, and because of travel restrictions amid the Covid-19 pandemic, they've been unable to jet across the world to see each other.
The source added: "Phoebe and Pete were last together in the UK in July but since he flew back to the States, he's not seen her. Obviously all the travel restrictions because of the pandemic have not helped.
"People can't just jump on planes and jet around the world when they want to. It has made everything more difficult. It was pretty telling when Phoebe headed to Croatia with her mates this week rather than going to see Pete in America."
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Phoebe, 26, and Pete, 27, were said to have been a "great couple", but those close to the pair don't think their relationship will "recover".
The insider told The Sun newspaper's Bizarre column: "It was wild while it lasted and they both really care for each other. But the distance has put a strain on them.
"Their mates think they make a great couple but the distance has made it completely unworkable. They had fun and will remain close but unless something drastic changes their relationship won't recover."