You can't exchange personal information prior to a confirmed booking, it is against Airbnb policy; all communication has to be done via the Airbnb platform so they will block any personal details you attempt to send to potential guest. It is also for your safety.
@Lauren28 If a guest is trying to get you to exchange numbers, it's likely a scam or an attempt to get you to do the booking outside the Airbnb system. Don't deal with these scammers. Report them (using the flag icon) and decline the request.