Family Sharing
Can I approve purchases and other family administrative things from a non-Apple device? I had family sharing working for my son's phone when I had an iPhone. Now I don't have another Apple device.
Question marked as
You need an Apple device. You said you do not use your old iPhone as your phone but did you discard it? If you still possess your old iPhone you can use it via Wi-Fi - if you have a Wi-Fi network - as your iCloud device to administer your Family Sharing network. This would include Ask To Buy.
If you have another adult in your group it is also possible to transfer Ask To Buy to them. Approve what kids buy with Ask to Buy says: The family organiser can give another parent or guardian in the group over the age of 18 permission to manage Ask to Buy requests. Only one adult needs to manage each purchase, and after it's been completed, the purchase is final.
Again, this requires an Apple device to achieve the transfer.