Booking a bus ticket on Highwaybus.com

Hi all,

The reservation requires a 9-11 digit number but from where I am, phone numbers are only 8 digits even though the website explicitly allows a reservation from my country.
Is the phone number necessary to make a reservation? Can I just enter a random number but login to my reservation page to get reservation details and get on the bus on the day itself?

https://imgur.com/Ow9ug3O

thanks.