What to do with old Mobile phones - Sony Xperia Z Ultra and Moto G 5S Plus

Have a lot of old smartphones lying in your cupboard and not sure what to do with them? Know from our experts what good use can you make of them or how to get the best price out of them and put them for sale.

I have 2 smartphones lying with me, one is Sony Xperia Z ultra and the other is Moto G5S plus. Both are in working condition but I do not use them for my normal use and have kept them in my cupboard.

Their screen had broken which I got repaired but the clarity and touch of original screen was lost so I purchased a new Nokia 8.1 at a very reasonable price and have put the other 2 as backup. I even tried to sell them to the shopkeeper from where I got it repaired but he was hardly paying Rs.2000 for each, so I denied selling it to him and brought it back to put it to some other use.

Now since then, I have not found a good use for them till now, I am asking technical persons to advice me on the same.
Can anyone who has put their old smartphone to good use share his advice with me here.