Hi,
I'm 10-yrs senior developer and have enough skills to create great projects on modern php/js stack - Yii/JQuery. I've done a lot of websites and services for my last client for 3 years and can implement both client and server sides of site/services using php, yii, jquery, angularjs, css3, fb api, mongodb etc. So I'm looking for long time relationship with good company and hope that will satisfied all your conditions.
I want to build backend server on php, precisely on Yii/Yii2 framework. This framework is good fit for your needs and your app will be easy to expand in future. Frontend (website, mobile version) I propose to built in modern Javascript framework - AngularJS - that is very modern and flexible framework. In this case we can use many same code for website, mobile version and app (iOS/Android on PhoneGap). Thats better than have separate website and separate app, because in future you must made change in code only once - and all must work everywhere.
Another way is full stack JS (Node.JS + AngularJS ) + PhoneGap for app. There more modern way of development, but take a bit more time and will cost a bit more. But, in future, you can hire only one developer, because all written on one language - Javascript.
Thanks,
Yurii