I ended up taking two phones, but used my phone for a fair bit of photography (especially earlier on). I was able to hook up the spare phone to the camera and download the photos via a USB OTG cable, and upload them to Google Photos whenever I was on WiFi (although I did do a lot of that after arriving home as WiFi was flaky in some hotels). I also had to buy another SD card while I was overseas as I filled the old one, and kept the SD card and my Aussie SIM in a secure spot in my bag with my passport.
As for camera photo quality, it's tough to compare. My phone worked better in low light, but my camera would focus way faster and had optical zoom. Had I a top end phone I probably would have just taken it and been happy, but I'm glad I took the dedicated camera. The added benefit is not wearing down the battery on my phone as quickly as I would have with just the phone.
Had I not run the risk of screwing things up by swapping microSD cards, I could have just swapped a microSD card into my main phone and uploaded on wifi from there, but one of my SD cards was a full size one.