The average salary of an English professor is $85,000 a year or so. The median salary is lower. The majority of people with PhDs in English who gradates in the past ten years are not professors, but contingent faculty, and their median salaries are around $50,000
The field under the title of “English” is, in fact, pretty wide and diverse. It includes sub fields like rhetoric, creative writing, medieval literature, gender studies, film studies, and many more.
English is, in fact, an excellent field as a major, since the skills that you learn there are highly useful in many fields. Creative writing, rhetoric, critical analysis, etc., are all amazingly useful in every walk of life.
However, most people with English degrees make more than English Professors, and people with English PhDs who have jobs outside of academia generally make more money than those who teach at colleges.
Moreover, to do a PhD in English you would first have to do very well in your undergrad, produce some amazing pieces of work in class, as you undergraduate thesis, etc. You then would need to compete with the top undergrads in the field for the graduate positions at the top PhD programs. It’s easier to be accepted to lower ranked graduate programs, but if a person wants an academic life, that is not a good idea. The lower ranked a program is, the the smaller the percent of graduates who get academic jobs that pay a decent salary.
A PhD requires some 6 years of research on an original topic in your sub-field. So you need to love research in, say, 19th century English literature, analysis of films, or something else related to the field. Professors do not teach people to read and write English. While colleges do have ESL classes, it is all taught by non-tenured faculty, though some may be full time, and the salaries are pretty low. ESL teachers in high schools make more and have better benefits.
I mean, if you really want to do a PhD in English, go for it, but it’s not a very lucrative career choice. If you like teaching, you can earn a degree in education and teach English in high school. Better pay, better benefits, and a lot more job security.
TL;DR An undergrad degree in English is an excellent degree and many employers like hiring English majors, but an academic career in English is not worthwhile in this day and age.