I want to know the difference between the two phrases "School of English" and "English school"? Can anyone explain to me please?
To answer simply, the difference between the two phrases is their specificity (level of specificness).
- A School of English denotes that the school teaches English.
- An English School may denote the same as the phrase above, but may also denote that the school itself is English which as @FumbleFingers notes in their comment to your question can refer to its location, or the nationality of its origin, its administrators or its attendees.
To illustrate with an example, the phrase English School of Mathematics is proper English (as in the language) describing an English (as in the nationality) School of Mathematics.