Im sure your husband will take precautions and be safe . It’s important to get that phone as it will have details of the last person he called on it and maybe texts. I’m sure your husband will find out where it was found . Call his ‘girlfriend ‘ back and explain everything ask her what hospital he said he was at and when ! He may of been telling the truth. Have you told the police that he is now without His phone and money ? Speak to his girlfriend ask her if she knows why he might be in London ( it’s not too far from some parts of Surrey ).
It’s good that the homeless person called you and is willing to give you the phone , I hope your son is found safe .
XXX