iOS 10.0.2 Phone App locks up and crashes

I’ve got an iPhone 6s and was an early adopter to iOS10. I’m not sure if the issue began with the iOS 10 upgrade or if it started with the more recent iOS 10.0.1 or 10.0.2 updates to iOS10. Here’s what I do know:

[Update] This issue was fixed in iOS v10.2.1.

[Symptoms]

After the Phone App is inactive for more than 1 hour, launching the Phone App will cause it to hang and eventually crash (just closes) after a varying amount of time in the “hung” or frozen state. During the time the Phone App is not responding, no touches register within the App. The home button still functions and app switching works as expected, but until the Phone App is terminated or times out and crashes, it remains unresponsive to user input.

[Research]

I’ve had enough frustrating moments with my Phone App that I finally decided to spend an evening reading a bunch of Apple discussions exactly what I was experiencing. Turns out there are a few threads on this problem, each of which describes the same underlying symptoms:

https://discussions.apple.com/thread/7671180
https://discussions.apple.com/thread/7666112
https://discussions.apple.com/thread/7671366
https://discussions.apple.com/thread/7681132
https://discussions.apple.com/thread/7679372

I had a theory about the issue being with Contacts rather than the Phone App itself from the get go. So, rather than following the suggested “wipe and factory reset” advice offered in most of the above discussion threads, I decided to actually do the work of testing my theory in an experiment to see if the issue was in fact related to the contacts used by the Phone App or Phone App itself. Here’s what I did:

1. Tapped Settings->Mail, Settings->Facebook, Settings-iCloud, etc. and for each synced account turned off Contacts Syncing.
   
2. When turning off contacts syncing on each account I opted to Delete from iPhone.
   
3. I did this until my Contacts App showed no Contacts.

Essentially now when I opened the Phone App, my call history and favorites just showed telephone numbers without any names. Similarly the same happened in the iMessage App. I then re-tested to see if the issue with the Phone App freezing would recur and it did not.

I waited 3 days and rebooted my phone several times to ensure that the Phone App freezing issue would not return. I can confirm that after 3 days of thorough testing with all contacts deleted from my phone and all sync accounts no longer syncing contacts, the Phone App did not exhibit freezing a single time.

[Resolution]

I then slowly re-enabled each synced contacts account one at a time and checked the Phone App for a full day after re-enabling each synced account.

Right away, I found that after re-adding contact syncing on an outlook.com email account, the issue with my Phone App freezing returned. Therefore I am tentatively concluding that either the issue is related to Outlook.com account Contact syncing or more specifically a perhaps malformed contact part of just my Outlook.com account. I am currently testing my iPhone with contact Sync for the outlook.com account disabled and have not seen the Phone App freezing issue. Once I have confirmed this, I will delete and re-create the account to see if the issue recurs.

Hope it helps,

TLDR: Try disabling just contact sync on any outlook.com email accounts on your iPhone.