Remember what Jake Wilson said about Bootstrap. Even though it is extremely helpful and can save time, you MUST understand what is going on behind the scenes. Be careful not to become reliant on its capabilities.
I know in class we mainly talked about Bootstrap as a framework, but there are also lots of php Frameworks like cakephp which makes writing dynamic and reusable php very easy much like Bootstrap does for html.
In Chrome, you are able to see what your website looks like on a mobile device by going into the developer console (ctrl + shift + j), and clicking the phone/tablet icon in the upper lefthand corner. Here is a tutorial on how to do this.
Link to getbootstrap navbar example here.
As discussed in class, most websites have the following goals in mind: