Will a JPEG of my accommodation suffice for my 60-day Thailand visa application?

No.

I was the same but I found it easier to do on a pc as opposed to my phone, you’ll get there in the end.

I recommend you get something that is refundable and cancel it once your visa is issued

Heather if you have booked accommodation through booking com Agoda etc you should have an email confirming this and it will contain a pdf at the end of the email. Go back online and go to the accomodation in Thailand section. You should have this saved if you have saved each section. Press the drop-down button and it should say upload press upload and then go to your email again, press the pdf part and it should upload automatically