Does the custodial parent have the right to block the non-custodial parent phone number?

Depends if you have an order for phone calls with the child.

If there is no court order defining each parent's rights and responsibilities, she can legally do whatever she chooses to do. You need to either get a court order establishing your rights or, if there is an order, you need to get the court to modify or enforce it. You should consult a lawyer for more complete advice about your options.

A lot of this answer will depend on the agreement, if any, between the parents. If the agreement requires, which most do, that you both keep your current contact information with each other, then the other parent is most likely in violation of a Court Order assuming that the agreement has been incorporated into a Court Order and no subsequent agreements and/or orders have invalidated it. If there is no agreement, then one should be put in writing and made a part of the Court's record and if there is no agreement between the parties, then there are certainly other options you can pursue, you should consult with a local attorney in person and as soon as possible prior to taking any action and/or omitting any action in regards to this matter.