My only camera is my cell phone which is a good one however the ISO only allows up to 800 when I've seen plenty higher on other cameras. Is that a sufficient number to work with once evening falls or am i gonna want and need a much higher ISO if I'm intering contest here n there?
This is up to you, if it works, it works... Unless it does not work.
This depends on the subject, on the situation, on if you turn on an additional light or not; if you are using candles or the bat-signal to illuminate your night scene. You could use a flash or not, you could need high speed for action, or you can create artistic looks with motion.
You could use noise reduction software, or leave the noise as texture.
There are newer sensors, newer cameras, and older ones too. Some high ISO on some cameras are just a marketing gimmick, some are really useful.
This is too broad. You need to decide.
The ISO equivalent, you see on digital cameras, is ruled by the chip actual pixel size, chip sensitivity and amplification.
- Pixel size: The larger the pixel is, the more light it can capture at time. It also averages the noise over the pixel area.
- Chip sensitivity: The more charge it can gain from a photon, the more sensitive it is and can handle low-light scenes.
- Amplification: The charge collected from each pixel is considered a continuous value, for digital processing one need to convert it to integer values. Amplifying the signal one can cover the bit depth of the image file. High amplification results in high noise.
Regarding your question "Is ISO 800 enough?" we shall look slightly deeper. The brightness of the resulting image is ruled by four factors: Lighting, Shutter speed, Aperture and ISO equivalent.
- Lighting: The brighter the scene, the more photons on the chip, the brighter the image.
- Shutter speed: The longer the time, the more light captured, the brighter image. Limits are: the longest - seconds, the shortest - milliseconds.
- Aperture: The more open aperture (lower F-number) the more light passing through the lens, the brighter the image. Limits are: Speed of the lens - the lowest possible F-number and the smallest hole the aperture can close.
- ISO equivalent: The higher value the higher brightness increment per captured photon.
Putting this all together, the answer to your question is strongly dependent on what you want to do with the camera in the night.
For stills, like you show in the question, you don't need to care for the ISO that much. Set it low (100 - 200), set the aperture to get the focal depth as you want and fine-tune the brightness by the shutter.
In action photo, you cannot play with shutter - you need to take it as fast as possible - so your only option is to open the aperture wide and try to get the rest with ISO.
If your question is more like rackandboneman's comment, My advice is:
Get as much as you can from your actual camera. Learn to push it to its limits. Write down what you (would) like shooting (portraits, landscape, macro, sky,...) and if your camera is honestly the limiting factor You will know what camera to buy and why.
Don't expect that new camera will automatically lead to "better" photos. You will need to learn how to use it (it is the old good fight among Nikoneers and Canoneers who is "better"). When doing significant step-up like going from iPhone to entry DSLR/mirrorless, you will lose a significant help from filters, presets etc. You will be responsible for the result. And that is the reason many photographers love their old gear.
As another answer said, I think it's entirely up to you and what you want to achieve.
In particular if you want to make night scenes look like daylight or something approximating it, then you are going to need very high ISOs and either live with the noise or have a fairly expensive camera.
But if you want to make night scenes look like, well, night you really don't need that at all. Instead you need to persuade your camera (or phone) that it should substantially underexpose (by its judgement) the scene so it looks mostly pretty dark. And to do this you don't need enormously high ISOs.
As an example: I shoot mostly film, and I don't really use film with ISO above 400. One of my favourite images was taken at night, hand-held, using ISO 400 film and a yellow filter, so with an effective ISO of 200. Now I'm sure it's not a sharp as it could be, but I made a bunch of small prints of it which I sent as postcards to people: it's an image I'm actually quite proud of.
In night if you will use high ISO it will not capture perfect picture that can be taken on phone. You should keep it to 100 or less and increase shutter speed and hold the phone still or use tripod.