Has anyone here interviewed people over the phone for freelancing or employee position?
What are some tips from your personal experience?

I just talk.

Don’t scare them, they’re nervous enough.
And give them time to answer in case they want to add some input.
And please make sure the questions are clear;)

When using the phone only, we're missing the entire non-verbal part of human interactions. So don't hesitate to be a little bit nicer than usual, as @just8littleBit suggested. It's easy to come off as cold otherwise.

Hackerrank or similar, whichever level of fizzbuzz us appropriate for the level you're hiring at, check that they're able to talk to you like a human, make sure you can understand them, make sure they can understand you, make sure they don't talk in run on sentences.

Remember that they are reviewing your company too, and how you sound reflects that, so try to sound like a human

Just make enjoyable conversation. It's that easy. keep it (mostly) centered around dev, the company, and most importantly: them. That's all you need to do.