The form-factor is a shape of a device that is physical structure of the phone. While manufacturers are continually coming up with new types of designs, there are different types of form-factor like bar, flip, candy bar, slide, qwerty.
A bar (also slab or block or slate) phone is the most common and basic phone, which has no moving parts. It is a single block, usually with rounded parts. This form factor is widely used by a variety of manufacturers, such as Nokia. Bar-type mobile phones normally have the screen and alpha numeric keypad all on one face.
A touch bar is nothing but a touchscreen phone, which is composed of minimal number of buttons with virtual keyboard whether numeric or QWERTY keyboard. Its display is of different types like TFT, LCD with capacitive touchscreen or resistive, transmissive.
A slide phone is normally composed of two section or more. One section contains the display and the another one usually contains the keypad. Slide designs allow the main display to be seen when closed, and are generally easier to open and close one-handed.
A flip model phone consists of two or more sections which are connected by hinges, allow user to fold or flip for more compact. When flip is open open, the phone's speaker and microphone are placed closer to the user's ear and mouth, which improves usability. When flip is close, its more portable to use.
A monoblock QWERTY phone is like bar phone, which has no moving parts. It is a single block but with QWERTY keypad. QWERTY is a standard layout for letter keys on text keypads, by which users can use keypad with their two thumbs to type text easy and faster.