Cannot sign in to iCloud on iPhone

Hi,

for a couple of days Im struggling to sign in to iCloud on my iPhone 5s.

After verification it return back to log in page and ask me to enter my log in information again and again.

It all start one day while I was scrolling through Instagram, the phone’s home screen crashed (black screen with loading wheel appear) and a couple seconds later the phone was back at home screen.

It start to ask me for my iCloud password and when I enter it it asked me again and again and I was stuck in this loop.

I’ve restarted the phone and found that Im signed out of iCloud, iMessages and Facetime pop up appeared informing me that I might me charged for activating them.

I guess the crash was due to low storage on the phone.

At the time of the crash the phone was on iOS 10.2 and later updated to iOS 12.3.1

After the update (may be also prior to it, but after the crash) I cant access AppStore.

I got internet connection over WiFi and Cellular.

I have also an iPad Pro 10.5” and I can access the AppStore over the same WiFi network and it is logged in to iCloud. To be honest Im afraid to Sign Out of iCloud on it and try to sign in again.

The phone is listed in my iCloud devices, but its icon is for space gray/black iPhone 5s, even though the phone is white/silver.

If I remove the phone from my iCloud devices it ask be for 2 step verification and after entering the code, it return to Setting and Im not sign in.

When I enter the log in information again, this time doesn't ask for code and it brings me back to Settings and Im not sign in.

I’ve tried following things:

• Resetting network settings followed by hard reset
• Resetting all settings followed by hard reset
• Turning off iMessages and Facetime, signing out of AppStore and signing out of Find My Phone app followed by hard reset
• Date and Time set to manual (it was auto at first place)
• Date and Time set to auto
• Updated the phone to iOS 12.3.1
• Logging in with my sister’s iCloud account

The only thing that left is to restore the phone and set it as new, but I don't what to go this way because I’ll loose iMessages and other messaging apps history, Photos in Camera Roll, App settings and etc.

Does anyone had this issue and how it was resolved?

Does anyone have any suggestions for resolving the issue?

Does the discrepancy of the color of phone and the icon for the phone in iCloud device list have something to do with the issue?