The two phrases with respect to and in respect of both mean regarding, concerning. While both are used in British English, in respect of is seldom used in American English.
With respect to your enquiry we can deliver the items by Friday.
The two novels are very different in respect of the development of their respective characters.
Both these expressions are used in formal writing. When we speak, we have other ways of expressing regarding, as you can see here.
To a non-native English writer, the use of prepositions in English is often confusing. In the phrases we are looking at here, we cannot change the prepositions and say, for example *in respect to (for the use of the asterisk see the comment at the end of this text).
To have respect for someone is to show consideration or respect towards a person or admire someone for their qualities, ideas, actions, etc.
She has great respect for her grandfather’s long experience.
I have no respect for people who keep interrupting others.