How to explain the reasons to change Phd. supervisor
You didn't say in what situation you need to explain this, which may change the answer.

If it is merely coming up in passing in a conversation, "It was not a good fit" is a good neutral way to give the general idea and leave it up to your interlocutor whether to pursue the topic or not.

If you are specifically asked for your reasons for leaving, a condensed 2-3 sentence version should be enough in most cases. Try to avoid placing blame, it is not a trial of who is right or wrong, you or your advisor. E.g. "our research interests do not align, I would really like to go more into topic B" rather than "he keeps making me do grunt work on things I hate". If you have academic reasons you probably don't need to go into the personal reasons at all, but if you do want to bring it up at some point, frame it as something like "our personalities do not mesh well". Stay carefully factual when recounting details. (This doesn't mean downplaying the issues. Think of a way to formulate it neutrally but still exposing the crux of the issues barefacedly.)

Generally, potential other supervisors will see themselves in the role of your current supervisor, so they will imagine that you will talk about them in the same manner as you will talk about your current supervisor.