On iPhones (iOS/Apple) the NFC-antenna is on the back of iPhones at the top of the phone. To read the NFC tag with an iPhone, place the top edge of the back of the iPhone on the tag.

On Android phones, the position of the NFC-antenna is dependent on the manufacturer of the Android device. Typically, the NFC-antenna can be found near the camera or in the middle at the back of the phone.  To read the NFC tag with an Android phone, place your phone over the NFC tag and hold it steadily in place. It is important to position the NFC-antenna in the middle of the tag (i.e. for Samsung devices the NFC-antenna can be found in the middle at the back of the phone).