The HTC U11 rear-facing camera sports what HTC calls a "full sensor auto-focus technology", which is the same dual-pixel phase-detection autofocus technology that is used in the Samsung Galaxy S8. In this technology, each pixel on the sensor has two photodiodes, which are used to calculate the amount of signal difference in the AF points. Compared to contrast-detection AF, the camera doesn't need to move the focus back and forth and compare images and it can get distance measurement almost instantly. This is why phase-detection technology is the preferred autofocus technology for subject tracking and when shooting in low-light situations.
I've also read DxOMark's HTC U11 review and there they also the dual-pixel phase-detect AF performance was one of the best they have tested to date in both daylight and low-light situations and gave it the score of 95 and mentioned that the AF performance was even better than the Google Pixel / Pixel XL and the HTC 10. By the way, the Google Pixel uses both phase-detection and laser AF, si it just made me wonder whether there is a need for a Laser Autofocus system where there is a dual-pixel AF system onboard. Laser AF is known to perform very fast up for subjects up to around 10 meters, but it's not that the PDAF is more limited than the laser AF when shooting subject at those distances.
I've also saw this UltraSpeed Autofocus test video done by gsmarena.com website. You can clearly see that the camera switches between AF points really fast, almost instantaneously.
The main advantage of having all points serving as phase-detection points is that the camera can track any subject across the entire frame, not just in a particular area, like in the center or like in other PDAF sensors where the phase-detect sensors use in a small portion of the pixels, not all of them. PDAF is useful when shooting a subject that move really fast across the frame, regardless of its position. You can trust on the HTC U11 autofocus system to make sure that the subject will appear in focus. You will get much less pictures with the subject out-of-focus.
If you have an older phone that doesn't utilize this type of advanced AF system like in the HTC U11, you probably know what I'm talking about. Sometimes you don't even notice that the subject is not in focus until you view an enlarged version of the image on the phone or when going over the photos on your computer on a large display. The subject might appear sharp in first glance on the thumbnail in the camera app, but it might be quite blurry when you zoom in to view it. The thing is that most of us don't do focus check for each photo we take. We just want to tap and get the picture and move on to the next photo. This is why you want a phone with an autofocus system like the one in the HTC U11.
Just keep in mind that the AF performance may vary depends on the subject, its direction and speed, the lighting, etc. Nonetheless, it's great to know that the AF system was already tested by one of the most reliable mobile camera websites and its autofocus system was given a very high score, so you know that you can trust on the HTC U11 autofocus to deliver the result you expect from a modern flagship smartphone camera.