it's all done locally on your device. vexl doesn't see your contacts or your phone number. also it doesn't touch your bitcoin or fiat. 

https://blog.vexl.it/understanding-vexl-security-privacy-and-building-a-web-of-trust-867710d4a6fe

it's non profit, open source and private...  

 Thanks for the clarification!! I was not aware of Vexl! Great to see there is another P2P platform for buying bitcoin!