What do you think about PHP trends in 2017?

Favorite changes in PHP in 2016?

None, as there have been only minor changes to the language during 2016.

Opinion about PHP 7/7.1?

Way better than 5.x, but yet again adding PHP Sadness with stupid shit like the declare(strict_types=1) flag.

5.6 support is about to end this year. Problems you think will occur while upgrading to PHP7/7.1 as it comes?

Zero. There are only 2 cases in which you'd have problems: you have to have either really crappy code, or to have intentionally ignored modern practices.
No, I don't care what your reasoning is for thinking that your now-broken-under-PHP-7 code is fine; this is the most painless to upgrade to major release I've ever seen. All of the BC-breaking changes are just common sense.

You think Frameworks like Laravel,Symfony, Yii will help keep PHP a major programming language?

No. If anything, 2 out of the 3 mentioned are having a bad effect.

Which framework is best from above 3?

Neither. There's no such thing as a "best framework", even if you mean best between a few select ones.