The two I know of are Google's Blockly (https://developers.google.com/blockly/) and Microsoft's Touch Develop (https://www.touchdevelop.com/), which is more capable as a standalone app development platform.

I've tried writing a small program with each on my phone and quickly grew frustrated. It just isn't efficient for me. I much prefer the familiar ground of using Python on Termux using Hacker's Keyboard, and, even then, only to tackle trivial stuff that a calculator can't quite handle.