Video size is simple arithmetic: bitrate multiplied by time. Resolution matters only through the bitrate the encoder spends to keep that many pixels looking clean. The numbers are worth memorising in rough form. A minute of 1080p at 30 frames per second is somewhere around 60 to 130 megabytes, depending on the codec. A minute of 4K at the same frame rate is roughly 190 to 350 — call it five times as much on the same phone. Sixty frames per second costs more again, though less than double, because most of any frame is the frame before it. Multiply out and the scale becomes real: an hour of 4K talking-head footage lands somewhere between ten and twenty gigabytes. That is not a rounding error on a phone. That is the phone.
Two decisions control the total. The first is the codec, which your phone largely makes for you: HEVC stores the same picture in about half the space of H.264, and modern phones default to it. The second is resolution, and the question to ask is where the video will end up. A vertical feed shows viewers something close to 1080p however much you give it, so 4K earns its cost only when you plan to crop, reframe or zoom in the edit — real reasons, but reasons you either have or do not. Choose deliberately: the app records 720p, 1080p or 4K at 24, 30 or 60 frames per second, and it only offers the modes your camera actually reports, so nothing on the list is a guess.
The other thing worth understanding is that a published video exists at least twice on your phone: the recording you made and the export you shared. They are different files with different sizes, and a storage total that lumps them together lies to you in both directions — deleting an export does not touch the take, and deleting a take does not remove the copy you published. Talk2Camera keeps the accounting honest: recordings are counted separately from exports and other files, you can see how much room is actually left, and the app warns you before the disk becomes the problem rather than at the moment it already is. That last part matters most mid-shoot, because the worst place to do storage arithmetic is between takes.
Then delete with the facts in front of you. Every take in the library shows its length, its size and its date, which turns guessing into arithmetic — three rehearsal takes at 400 megabytes each is a gigabyte you can have back in ten seconds. Tick several and remove them together; the confirmation states plainly that exports are separate files and stay where you put them, so clearing raw takes never touches a video you have already published. The rule of thumb worth keeping: delete rehearsals freely, but keep the raw take of anything you might re-cut. An export is a compressed copy, and every edit made from it costs a generation of quality that the original would have kept.