I am new to php development and want to choose a single php framework which is easy to learn with followings in mind:-
This probably isn't the appropriate forum to ask this type of question, but I would recommend you to take a look at CodeIgniter anyway. It is known for being easy to learn (it has a nice to follow documentation), don't leave you overwhelmed with a lot of features you don't know if you are going to need it, and manages to be considerably fast.
WordPress is a content management system not necessarily a framework. Since you are new to PHP I would direct you away from frameworks towards a CMS like WordPress. While WordPress will get you off your feet developing fast you will be exposed to a code base that is dead brilliant.
This question never seems to end, blogs, forums, seminars, trainings etc etc.
Major frameworks that i know of
I have been using Cakephp for 3 years, i love it but since as you are beginning i would say go with "Yii". Cake is very hard to learn without supervision. Many of my team members over the years when left without supervision have struggled to converge on projects.
Whereas for Yii, i have seen