@Betty567 You cannot write off 100% of your cell phone unless you have a phone exclusively for handling your AirBnB business and have a separate phone for personal and other business use.
You also don't write it off 'by the day.'
For taxes (in the US), it's all about percentage of use. I imagine it's much the same in Canada.
I'm self-employed. I tell my CPA how much of my phone use is personal and how much is business. Since it's really hard to pinpoint, most people just use 50/50.
With a car, you can track usage by mileage. With a cell phone, not so much.
Honestly, I've never written off any portion of my phone for my AirBnB, as there's not really a need to use it. I can access the platform via computer or phone (or tablet), but I've honestly talked to a guest once or twice over the 4 years that I've been hosting. I keep everything on the AirBnB platform via messaging.