Can a hotel charge me for reservation with just my mobile number?

A hotel will not take your reservation without a valid credit card number.  Period.

Canceled reservations cost the hospitality industry millions each year so none will take a reservation without a credit card because you WILL be charged for a no show or canceled reservation.
No reputable hotel chain will accept cash alone either.
You still must give them a credit card so that if you damage the room ore steal something they can charge the card.