NFC read range for contactless cards is usually 0-4cm. For mobile handsets they typically will not read past 2cm. Also, depending upon the reader and placement in the field, you could be collapsing the field. There is also a "sweet spot" which the vendors usually put in the middle of the phone. (It's where the antenna will transmit the best.) If the phone doesn't work, take it out of the field and place it back into the field after about one second. Try to match the middle of the phone flat with the NFC emblem. Repowering the field typically takes ~1500ms. Anything metallic could interfere with the RF. Hope that helps!