Sounds like the seller is planning to ship by UPS or another courier.
Plan to pay the deliveryman Canadian tax, duty, and the courier's customs brokerage fee of $25 or more on your doorstep.
Couriers want the phone number so they don't waste time trying to deliver to an empty house. USPS/Canada Post is cheaper (CPs service fee is $10 and their packages are often skipped by CBSA at the border, meaning no doorstep charges). CP leaves a note telling the absentee to call at the local PO the next day.
You can supply any number. If you are not at home during the day, give the phone number of your work, or your spouse's work. Or a cell phone.
There is no danger in doing this.
