The cheap upgrades that show up on camera
Face a window or a soft lamp. Do not sit under a ceiling light. Clean the lens. Prop the phone at eye level, not at your chin. A cheap clip-on mic or a wireless mic near your mouth beats the phone mic across the room.
Lock exposure and focus. Shoot 4K if you will crop, otherwise 1080 is fine and easier to edit on the phone. Turn on captions in the edit. Export the vertical file, then make the cover frame a readable picture, not a random middle second.