The short answer is no. You are free to hold your phone any way you choose. The long answer is a resounding yes. We are fortunate enough to live in a time when huge amounts of bandwidth are available to 90% of the homes in America. To take advantage of that, entertainment producers decided to add huge swaths of real estate to the left and right sides of your TVs, computer monitors and handheld devices. TVs are no longer square, thus, devices that take photographs and record video no longer record square media. The most common aspect ratio one can expect a TV or monitor to display is 16:9, which can be thought of as 16 units wide by 9 units tall.
Why not take advantage of all that extra space? Turn your handheld device on it’s side. It won’t mind. (does not apply to dedicated cameras!)