Much like every class of device nowadays, you may opt to approach the phone-to-projector connection process in one of two ways, broadly speaking. Since all good projectors have HDMI in, you can get a USB to HDMI cable or adapter. These are available for every version of USB, so check your phone and pick the right one. Once connected, simply change the source on your projector to the relevant HDMI port and you’ll see your phone’s screen displayed. If your phone or tablet have a mini HDMI out, even better, though you’ll need a mini HDMI to HDMI cable.
In most cases, it’s good to use a USB to HDMI adapter plus an HDMI cable. A setup like that will cost anywhere from US$30 to US$80. Regular USB to HDMI cables are simpler but may compromise quality because they lack the adapter to negotiate the USB to HDMI conversion. USB to HDMI cables range from US$10 to US$50 in price, depending on brand. All prices as of summer 2020.
The wireless option may be more appealing if you don’t want added cables all over the shop. If your projector has Bluetooth, then pairing it with a modern mobile phone or tablet is easy. Since Bluetooth isn’t prevalent on home cinema projectors (but standard on quality portable projectors), another good way is using a third party media box or streaming stick. Roku, Fire TV, Apple TV, or Chromecast will do just fine. All have Bluetooth and easily pair with mobile devices. Once paired, the media box or stick sends phone contents to the projector via HDMI. As all major media and streaming sticks have full size HDMI out, there’s no need for adapters: they plug in directly to the HDMI in on your projector.