What do you mean by 'unsync phone number'? Is your iPad on your account as a separate line with its own phone number? Is your iPad using the Message+ Integrated Messaging with your phones' phone number? More information of your issue/scenario is needed.
Please let us know if this guide is helpful: https://support.apple.com/en-us/HT204074
Feel free to send us a Private Note if you need further assistance.
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