back out (of something)
Definition: to decide not to do something you had previously agreed to do.
(This phrasal verb has more than one meaning)
E.g.1: You promised you would do it! You can’t back out of doing it now!
E.g.2: When he climbed up to the highest diving board and looked down into the water, he wanted to back out, but he knew his friends were watching.
This phrasal verb can’t be separated.