Can you teach a youth group of 15 to index on their phones?
To Index you could use the web browser on the phone. But the screen on a phone is very small. It would be awkward to see the data entry area and also to see the image. You would have to be moving to and fro continually. I wouldn't recommend it, especially for newbies.
This knowledge article explains the requirements for Indexing on a tablet.
Note also this line "At this time, we are unable to support indexing from smart phones due to their small screen size."
The BYU Family History Lab has a mobile "indexing app" for phones.
Read about it here: https://www.facebook.com/BYUrecordlinkinglab/
Access it here: https://fhss-priceweb.byu.edu/Home/Record?fbclid=IwAR3rQdI1tzakzyYCWu-YQBLPqwwpDkLOnEwqYphMxrQBmEp4zOu03i2INnQ