[Google Pixel XL Questions & Answers] exclusionprinciple:
I've had both of those problems on my Pixel 2 for quite a while now along with a new one :

Not able to answer calls from the notifications issue -

The easiest workaround for this is to just tap on the notification itself (Not Answer/Decline button) which will take you to the blue call screen. Swipe up from there.

I feel this has something to do with Android itself rather than just the phone app. I have similar issues with the play/pause button for the play music active notification. It simply does not work when I press it at times. It does not even register the click. But then the process is delayed and gets triggered after quite some time. I've had my speakers go off with my last played song during work meetings randomly as a consequence of the random delay. The only workaround is to close the play music app and reduce media volume.

I've also noticed the clock in the notification bar to stop randomly at times. I can confirm that this is just with the notification bar because I have a clock widget that displays time on my home screen and that's always correct. Even the one on the lock screen shows the correct time always. I've run into critical issues after getting the wrong time from the notification bar and have mentally conditioned myself to always go to the home screen to get the correct time.

Not able to make calls issue - (The only sure-shot method to make a phone call during an emergency is to enter Safe mode.

This is something I still haven't figured out the solution to. Google support just keeps asking me to factory reset. I don't want to setup the whole thing again from scratch after I've heard others complain that a reset does not solve the issue.

The best work around for this is restarting into safe mode every time you want to make a call. Yes. There was a point in time a few days back, where I would automatically reach for the power button as a reflex to enable safe mode, whenever I want to make a phone call.

One more tip to note is, you should press the call button only once. Even if it doesn't trigger a call immediately, don't press it again repeatedly, but just wait. This reduces the delay and the call starts in a short time. This has worked for me recently.

I was excited when I got the march update two days back, hoping it would solve all these issues. But nope. It's still the same.

New issue(even in safe mode) - It takes 13 SECONDS after the call gets connected (when the other person picks up - essentially when the timer starts) for either of us to be able to hear anything. A lot of people won't wait for that long before they hang up.

And this happens randomly, even if the call is an incoming or outgoing one. It's the same even in safe mode. Tried all the cache reset and everything. Disabled phone permissions for almost all the apps except necessary ones. I don't use that MBA app either. This issue also can be found in the comment section for the phone app.

Are there 3rd party dialers that can be used apart from the official phone app? And does it work? Truecaller is useless because the call is still directed through the official phone app. I'm on Reliance Jio network, sadly their Jio 4G voice VoLTE dialer is automatically disabled for phone with native VoLTE.

It's driving me nuts now. Really bad experience from a flagship. Oh, and wait, all these are apart from the other issues like that annoying high frequency noise that's still not rectified. And my Pixel 2 charging adapter stops working randomly and then gets back to normal after a couple of days. Been using my Nexus 5X adapter as a fallback. But yeah, that's a story for a whole other post. Nothing as critical as the phone call issue.

I've had all the phone call issues from around december~january. But, I'm very relieved to have found this thread after a constant search for the same on reddit and a lot of other blogs.