I know hot wallet, cold wallet. But...in case i would use the hot wallet on an iPhone that has installed only the wallet and have internet connection...would it be possible to get hacked in a way if only that would be the use for it?
You mean you will use the iphone only for the wallet and not use it for any other purpose, but in a way it would be connected online? Why not sell the iphone and use the money gained from it to buy a hardware wallet? Like Passport which is an airgapped hardware wallet with the use of QR code.
If you do not use online device but just for wallet purpose, and you disable all apps not to install apps, and you disabled the app store not to download anything other app or update anything, and you are not using the online device for file transfer and the likes, this will increase your device security, but it is still online and you can make a little mistake that can lead to loss of your coins.