No, you have registered by signing up with Google and hence phone number is not mandatory for you. You don't have to share your mobile number to withdraw money. Since you haven't registered using the offer link, you wont get the $50 offer.
Welcome to bitcointalk. I tried to visit your site and saw a good design.
Where are the Google options? Because when I am on the homepage, I only see a registration form and need to fill all of the things on that form. I also see that writing a phone number is a must so I suggest you remove it from the registration form because not many of us want to share our phone numbers.
Maybe you can add TOS for your site, so we know what to Do and Don't. By adding that to your site, people can read it and not try to break the rules. I hope you can also add an explanation page on the site so the potential visitor can know what exactly they need to do after they register.