Similar in terms of the 'time travel' aspect and the two main leads trying to change the outcome of certain things. They both go back to the '80s.

A big difference between the two is that in 'Life On Mars' the main lead goes back with his entire body, that is to say, he's there while his younger self is there as well. There are thus certain things he can't fix, since there is a paradox in play here.

In 'Boku dake ga Inai Machi' the main lead goes back in time in a completely different way. He goes back to the time he was a child and is IN his own 11-year old body. He can create different timelines, so the before mentioned paradox does not come into play in this drama.

They're both about men who seemingly don't care about anything slowly but surely starting to care about children that aren't related to them. Though in 'phantom detective' the main characters starts caring about two sisters, whilst in 'the man from nowhere' he starts caring about one little girl.

Plot-wise these movies are nothing alike. I would say that 'phantom detective' has a lighter tone than 'the man from nowhere', though.