@Randall99 Of course you can contact the host without a reservation. You use the "Contact host" button on the listing to send an Inquiry message. Or if you have already exchanged a message with the host, you just continue to message on that message thread.
And as a new guest with no reviews yet, I suggest you fill out your profile information, verified ID, and a real profile photo. You will find very few hosts willing to accept a new guest with no reviews who hasn't bothered to upload a photo, verified ID, and no profile write up.
But you need to contact Airbnb customer service about the system not accepting your phone number. The host can't do anything about that.