If you only have a LoopPay Fob, then the answer is no, You need your LoopPay device or Fob to transmit payment.
However, you can pay with the Fob detached from your phone, all by itself. That's called Button Pay and it uses your default card. You can learn more about it here.
There are other LoopPay device solutions for paying with your Phone - check out the LoopPay ChargeCase, or the LoopPay Card or CardCase at LoopPay.com.