@markp1-
Premiere/Premiere+ (model numbers below 4620) are lower end units with single band Wi-Fi radios that only support the 2.4 GHz band.
Be sure your phone's Wi-Fi hotspot is set to use the 2.4 GHz band, and not the 5 GHz band.
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X