MacBook as WiFi extender With AirDrop it seems that my MacBook Pro can have multiple Wifi Connections, so can I connect my iPhone to my Macbook at the same time as the macbook is connected to a Time Capsule's Wifi network.

I have both 5GHz and 2.4GHz Wifi in my house, and the 2.4GHz only just reaches my room, whereas the 5GHz signal is much better. Sometimes my iPhone cant connect to the 2.4GHz network without moving closer to the base station.

Is it possible to use my MacBook as an extender, so that my phone can connect to the Macbook and then use it's 5GHz connection, and it won't drop out and become unconnectable?
According to Dori's answer in this Apple.SE thread, what you're looking for is not possible:


  In order for a Mac to create a local Wi-Fi network, it needs to have a
  wired Internet source.


More information can be found in this Apple Support KB:


  
  Choose Apple menu > System Preferences and click Sharing.
  Select Internet Sharing and click the checkbox if it isn’t checked.
  Choose the Internet connection you want to share from the “Share your connection from” pop-up menu. For example, if you’re connected to
  the Internet over Ethernet, choose Ethernet.
  Select how you want to share your Internet connection in the “To computers using” list. For example, if you want to share your Internet
  connection over AirPort, select AirPort. If you share your Internet
  connection using AirPort, click AirPort Options and give your network
  a name and password.
  


You'd need to hook your MacBook up to a wired connection before you can share Wi-Fi via Internet Sharing.