Based on your description, it seems that the antenna's standing wave ratio is too high and not properly adjusted. Furthermore, the use of an unbalanced antenna (such as a GP or end-fed antenna) may be causing common-mode current interference with the phone's NFC, and also interfering with the computer's USB port.
Measuring the power of a shortwave radio station involves using a dummy load, not just a simple load. This is done without any antenna tuning or matching devices, and directly connecting a power meter or standing wave wattmeter to the input of the dummy load. For a 100-watt shortwave radio station, it's recommended to use a 50Ω standard RF dummy load with a capacity of 200 watts. If FM is not used, the radio station operates in CW mode, continuously pressing the key, rather than speaking into a microphone.
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