Four links join a PC to a phone screen, and each one can be the reason nothing shows. Here is what every link actually does.
When a phone-as-monitor setup fails, people blame the app. Almost every time, the fault is in the chain - a cable, an adapter, or a card that does not do what its box promised. This page takes the chain apart link by link, explains the two terms that matter - UVC and OTG - and tells the truth about buying cheap capture cards.
The HDMI cable is the simple part: any working cable will do, because it only carries the picture from the PC to the card. The capture card is the clever part. Inside, it converts the HDMI signal into a USB video stream in real time.
Two warnings about the card itself. First, it is one-directional: HDMI goes in one marked port and USB comes out the other side. Plug the chain backwards and you get a black screen, not damage. Second, the card is powered from the phone through USB - there is no separate power supply, which matters for battery life on long sessions.
UVC stands for USB Video Class - a standard way for a device to say "I am a camera" to whatever it plugs into. Because it is a standard, the phone needs no special driver for the card: any app that can open an external USB camera can open the card's feed.
This is the one specification you must see before buying. A card that is not UVC may work only with its maker's PC software and will show nothing on a phone. Reputable listings say UVC or "driver-free" clearly. If the listing talks only about recording and streaming on a computer and never mentions USB camera compatibility, be careful.
OTG - USB On-The-Go - lets your phone act as a USB host, the same role a computer plays when you plug in a pen drive. Normally a phone is a guest that gets charged and copies files. In host mode it powers and controls the device plugged into it.
The OTG adapter (or an OTG-capable USB-C hub) is what flips the phone into that role. Without it, the phone and the capture card both wait for the other to take charge, and nothing happens. Some phones also hide an OTG switch in settings that must be turned on, and on a few brands it turns itself back off after some idle minutes - a classic cause of a setup that "worked yesterday".
Budget capture cards are a genuine lottery, and this page will not pretend otherwise. The same-looking card is sold under dozens of names, and the printed claims are often fiction:
For BIOS screens, server checks and setup work, even a modest card is enough - text at 1080p30 is clear and readable. Buy from a seller with easy returns, test the card the day it arrives, and judge it by the feed your app actually reports, not the box.
The video shows the real chain being plugged together - watch which port takes which cable before you buy anything.
Watch Full VideoUsually not. A plain charging cable connects the phone as a guest device. The capture card needs the phone to act as host, which is what the OTG adapter enables. Some USB-C hubs with OTG and charging pass-through do both jobs, and they also solve the battery drain problem.
Not necessarily broken - this is the normal trick of budget listings. 4K is often the maximum input the card accepts, while the USB feed it outputs is 1080p or less. For setup and admin screens 1080p is genuinely enough; for recording gameplay you would want a better card.
It can, but every extra adapter is another connection that can fail or slow the link. Keep the chain as short as possible: card into OTG adapter, adapter into phone. Long adapter chains are the first suspect when a working setup becomes unstable.