Is it possible to review an iPhone app from browser?
No, it's not something Apple puts up a web interface to allow reviews off device.

However, you can connect any USB keyboard to your iOS device using a USB adapter and most bluetooth keyboards work very well if you have one handy to try pairing.

I too find myself longing for a proper keyboard when writing due to years of habit forming. Bringing your preferred tool to iOS makes it much easier to compose even with the small screen in my experience.

Worst case, pen your review in iCloud version of notes / pages / wherever and save the text to the device so it can sync over or just be there on the storage and copy/paste if you can't find a better workaround.