In , nospam suggested:

Setting his phone to use a static IP while connected to his home
network, would be a good idea

it's a horrible idea because he'd have to change it every time he
leaves the house and back again when he returns.

On Android, the IP address on the phone is set "per access point"!

Look at the original post again where the Android settings were shown:
Android: Settings WiFi {AP SSID} Modify network config
IP settings Static IP address = 192.168.1.15

Notice that the "static" setting is set *per access point*.
That means the "static" directive only applies for *that* access point.

There is a caveat which I'd like to ask the cognoscenti here to explain:

Interestingly, in practice, at home, since I have more than half a dozen
access points, you'd think I need to make the static setting for each
access point at home - but - in practice - so far anyway - the phone has
remained on the same IP address - even after multiple boots of the
computers, mobile devices, and router.

Why does it work so well (without me setting the phone's IP address to be
static for *all* my access points)?