Hi there,
So, You get it’s only a TAG, GREAT! SO the Mobile phone you are using is it BLE5.0 compatible. Most Older Iphones are NOT. So there’s that.
Have you tried or used the NFC_tools APP ? Allows to program a real tag and read them as well. A good way to test function. Works well with a matched antenna.
HTH
GL 
PJ 
this is the DEV board antenna…