...Is probably the right answer.
Unfortunately, if you want a phone that actually works these days, you're basically stuck with iOS or Android devices, and all the junk that implies.
If I could buy a modern dumbphone that just works as a phone, with decent components so it has good reception and reliability, and ignore the whole smartphone fiasco altogether, I'd do it in a heartbeat.
Doesn't the YouTube app still rely on Google Play Services?
Anyway, if you still want to watch YouTube without Google, I'd recommend NewPipe on F-Droid. [0]
It's awesome. You can download videos to local storage for later watching, play music headless in the background, and there are no ads!
edit: or you can make one http://zerophone.org/ which also has plans to crowdfund some pre-built phones
If you want anything at all beyond basic features, like say a dual SIM option for use when travelling, you're straight into high-end smartphone territory, even if you actually have no interest in the so-called smart parts of the device.