Greetings Lapa_ua,
The following steps may be able to assist you with getting your iPhone 15 connected to your LG 24 Ultrafine:
Connect iPhone to a display with a cable
"With the appropriate cable or adapter, you can connect your iPhone to a secondary display, like a computer monitor, TV, or projector.
- Depending on your iPhone model, plug a Lightning Digital AV Adapter, Lightning to VGA Adapter, USB-C Display AV Adapter, or USB-C VGA Multi-port Adapter into the charging port on the bottom of iPhone.
- Connect an HDMI or VGA cable to the adapter.
- Connect the other end of the HDMI or VGA cable to the monitor, TV, or projector.
- If necessary, switch to the correct video source on the monitor, TV, or projector. If you need help, use the display’s manual."
We hope this helps.
Have a wonderful day!