I bought a very cheap Vivo Y52 mobile phone. It was £169 from Amazon, and has a 6.58" screen, 5G, runs Android 13, does all I need it to do.
Like you, I didn't want to risk my main phone (iPhone 13 Pro Max) camera, so went for the cheapest 5G Android I could find. Its not technically waterproof (think official IP ratings are too much for the cheaper brands to bother with), but I've been in rain with it with no issues (fairing protects a lot on my bike), and I bought a small plug for the headphone socket to stop water ingress there.
No complaints, does everything I need it to do, big enough on my 1200GSA without being tablet size. I have stashed the Wunderlinq in my fairing and removed the OEM navigation mount and use a QuadLock for the phone mount.....with a cable up from the Wunderlinq to charge the phone.