I think I was tagged because I'm a trucker too, but this is outside my wheelhouse. The only time I've casted anything to a tv was at home and on Wi-Fi, so I don't know what sort of non-Wi-Fi options are possible. The only thing I can think of would be transferring the videos to a thumb drive and plugging that into the tv. But even that may be questionable because not all tv's can read from a thumb drive, and then you have concerns about file type compatibility. Another option would be a USB media player that you can plug a thumb drive or (micro) SD card into, which outputs to HDMI to the tv. I haven't used anything like that but saw quite a few options on Amazon.
Sorry I can't help more, but that's about the only options I can think of. If you really want a wireless casting option, then his only option may be to buy a cheap Wi-Fi router to bring on the truck, and some of them may be cheaper than the USB media player anyway. It wouldn't have internet unless you get a true 4/5G enabled hotspot, but would allow the phone to cast saved videos to the tv if the tv has Wi-Fi built in. The audio only issue with YouTube and the like is probably the phone treating the tv like a Bluetooth speaker. Getting true online streaming to it would require either a hotspot through his carrier with an internet subscription, or a subscription for fast hotspot connections on his phone.