What App can control smartphone remotely?

So I help friends and family remotely for their PC using

Teamviewer and LogMeIn

We know some people that are technologically not advanced. So it's easier for me to do it for them than it is to spend hours on the phone explaining.

What app could I use for a smartphone to do the same similar thing where I can use my smartphone to control their smartphone?

Which is the best Free one?

Does team viewer have app for smartphone to smartphone

For example somebody ran out of space and I know how to clear it. They do not.

Thanks in advance

I haven't read through the information, but you provided the pointer::