Portrait Orientation Lock not working after update iOS 11.2.1

It's very strange that you are having this issue in two different iPhones, and this makes me think that is not a hardware issue. It looks like some of your settings are not appropriate (check if zoom is set to standard, and/or font size is normal).

To my knowledge, this is the only support guide that you can use.

If the screen doesn't rotate on your iPhone, iPad, or iPod touch - Apple Support

And I don't think this is related to iOS 11.2.1 (I would have read about this in some threads of this community),

But again, if the issue still persists, contact Apple at: Contact Apple Support

Regards

Giulio

Depending on your iPhone model, I would try a forced restart, following the steps here provided:

• On an iPhone X, iPhone 8, or iPhone 8 Plus: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then, press and hold the Side button until you see the Apple logo.
• On an iPhone 7 or iPhone 7 Plus: Press and hold both the Side and Volume Down buttons for at least 10 seconds, until you see the Apple logo.
• On an iPhone 6s and earlier, iPad, or iPod touch: Press and hold both the Home and the Top (or Side) buttons for at least 10 seconds, until you see the Apple logo.

Test it.

If nothing helps, have your device inspected at the nearest Apple Store or Authorized Service Provider.

Regards

Giulio