How is Planar Inverted F ( PIFA) Antenna manufactured?

I want to know if the following figure is a typical structure of PIFA or not?

Is there usually air substrate between top plate and ground? Where is the high dielectric constant substrate then?
How is it manufactured and then fitted in the mobile phones? I want to design one but i was wondering that absence of a solid substrate should damage the structure , right?

In a typical PIFA, the ground plane is large compared to the radiating "F". Otherwise, it works more like a dipole with built-in impedance transformer.

but in literature, they put no substrate between top plate and ground plane. what if I want PIFA printed on a flexible PCB??
can you please explain this " Otherwise, it works more like a dipole with built-in impedance transformer."

There are many varieties of the PIFA. You can make them with air dielectric and non-air dielectric. Adding dielectric may increase the loss significantly, reduces the physical size and reduces the usefull bandwidth.

Instead of air a low-dielectric constant foam can be used, sandwich of FR4 with low dielectric foam, or an insulating post supporting the (rigid) radiator.

If you want the PIFA on flexible PCB, distance to ground will be too small (for up to some GHz operation) so that loss will be excessive and bandwidth may be too small.

For more specific feedback, provide us more details.

I want to work on 1.5GHz and I realize that i either go for printed IFA or Planar IFA ( which would mean having via holes)
The material to be used is double sided with substrate height of 0.1016mm (4 mils between two 1 oz copper layers). I am intending to keep the back side of flexi PCB as ground which will not be much greater in size

which other types of antenna are less dependent on ground plane? (if any)

Do you mean that the ground is 0.1mm below the radiating element? If so, this is not going to work, unless you can accept very high loss (that means very low radiation efficiency). Don't limit yourself to PIFA, there are many other ways to get the waves from the air, or to get them into the air.

If ground area have same size and is covering about same area as antenna, can not any monopole solution be used as total antenna is depending on ground as counterpart for the second, in ground mirrored monopole part.
These both parts can not occupy same PCB area. PIFA/IFA are monopoles, which together with length in ground create a dipole.
Slot antenna directly in ground layer do work relative well even at a flexible PCB. Area around a slot antenna can be used for components, but not directly above or below the antenna.
A full wave loop can be designed to follow outer edge of PCB. As it is a full wave, it is a long antenna, but most of the occupied area inside of the loop can be reused for electronic circuits, with low antenna loss.
Common ways to shorten antennas and still keep them resonant are by using ceramic dielectric or by tuning with discrete components and stubs.
A common antenna type when small size is more important then performance is a electrical short loop antenna. Often found in remotes for cars.
A dipole antenna electrical length can be much shorter then lambda/2, it is still an antenna, just not as effective.