If I understand, since updating to iOS 11.2.6, the phone becomes unresponsive. There doesn't seem to be one specific thing that causes it, and it happens across multiple apps. I rely on my own iPhone for pretty much everything, so I know it's important that yours works without issue. I'd be happy to help!
Based on what you've described, I would recommend first force closing any open apps ( How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support ), and then restart your iPhone ( Restart your iPhone, iPad, or iPod touch - Apple Support ).
Once your iPhone is back on, check for any available app updates. To do this, open the App Store app, then tap Updates > Update all (or, if only one update is available, tap Update next to the app name).
If the issue continues after the above steps, I would next recommend you first back up your iPhone ( How to back up your iPhone, iPad, and iPod touch - Apple Support ) and then use the "Put your device in recovery mode and set it up again" section of If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support to reinstall the iOS software. While the title of the article doesn't match your issue, the steps to reinstall iOS are still relevant, and doing this can help clear out hiccups or issues that may have happened with the original update by installing a new copy of the iOS software onto your device. It shouldn't remove any of your data, either--but do make the backup I mentioned ahead of time, just in case.
Best!