Hi thecrescent,
Just saw your post.
Not sure if it is too late.
Years ago I used an app called StageCaller
https://www.disappointedpig.com/projects/stagecaller/
Works on both iOS and Android.
It does exactly what you want.
It was a bit problematic for us due to WiFi issues in the venue and the number of devices we were using, I think we had eight phones.
There was a small cost for each device at the time.
I do not think it is being actively updated anymore but it is worth having a look.
Good Luck,
Lindsay