I want to design a digital filter with the following phase response in MATLAB. i.e. at 1kHz, the phase response should be 9 degrees, at 2khz phase response should be 18 degrees ,at 3kHz phase response should be 27 degrees, at 4kHz phase response should be 36 degrees and so on upto 8kHz.How to design such filters having desired phase response?
What you describe is a linear phase. Assuming that your sample rate is 48 kHz, you can implement this simply with a delay of -1.2 samples.
The tricky parts here are that the delay is negative, i.e. the filter is non causal and that the delay is fractional (and not an integer number of samples).
This can all be done, but needs to be carefully tailored to the specific requirements of your application.
Here is an excellent article on the topic: http://home.agh.edu.pl/~turcza/sr/Splitting%20the%20Unit%20Delay.pdf