How to downgrade from iOS 26 to iOS 18 on iPhone 15 Pro Max without a laptop?

How to uninstall iOS or iPadOS beta software - Apple Support

So you din't bother to read ANYTHING that was provided to you when you joined the developers beta?

Bummer.

You're going to lose data. No two ways about it. The only way to avoid that is to stick with the buggy, unstable beta version until the final version is released in the fall.

1. You'll need a computer, but not necessarily a laptop.

2. This is only possible if you backed the data up before installing the beta, or are willing to go without it until reinstalling a beta or released version of 26.

(260516)

How can I do that without a laptop?

You don't need a laptop, but you do need a Mac or a PC.

I don't want to lose any data.

Did you make an "Archive" backup on a Mac of your iPhone 15 running iOS 18.....before.....you installed the beta iOS 26?

It sounds like you did not, so you should expect to lose the data on your phone when you revert back to iOS 18.

Amawah wrote:

I have not backed up the data to any laptop or computer. So what's next?

Is it possible to come?

iOS 26 is so slow

Since you are clearly NOT a developer, what on earth possessed you to install iOS 26, which is currently for developers ONLY. Jumping off a cliff without a parachute usually has bad results.

Since you didn't read the documentation about installing Beta releases on your phone and you didn't do an Archive Backup to your computer, you can restore your phone using the directions provided above, BUT your data will be gone and there is nothing you can do about that. Things you normally sync with iCloud, such as photos and messages, will redownload to your wiped iPhone, but everything else will be gone.

Beta software is inherently buggy. The ENTIRE point of being a beta test is to uncover the bugs and report them through the proper channels Apple provides. Apple specifically warns to NEVER install Beta on your primary device. This is a painful lesson you'll hopefully learn from.

Amawah wrote:

There is nothing more important for me than my WhatsApp messages, and my photos and files (on 'Files' app).

I can back it up all to my iCloud. But there is a problem with my iCloud too.

You see, I downgraded from the 200 GB Version Of iCloud because apple shows it that they'll charge PKR 800 for the 200 GB space where the actual cut from my bank account is PKR 2,800.

I am from Pakistan

You cannot do a backup to iCloud now. You needed to backup before you installed iOS 26 and even then that backup MUST have been made on a computer.

Sorry, but this is a problem you caused for yourself and we can't help you. As I suggested, this is going to a painful lesson you'll hopefully learn from.