Hi there, 

First, welcome to the community. 

What you are trying to achieve should be possible in theory at least but will need a bit of custom coding. 

You need to store the phone number, insert it in the pixel and then fire the pixel. 

Do you know how much control you have over the firing of the pixel?

My team and I have written dozens of custom Unbounce integrations and scripts so if you want, reach out to me with a bit more details: h@revise.cc

Best,

Hristian