Is there a single word for someone who loves the English language? Is it understandable to use Englishphile? Has the suffix -phile been used correctly?
You have used the suffix correctly, but I don't believe there is such a word. If so, it is not commonly known and used. An Anglophile is someone who loves England and English things (not America/American), but this term does not specifically refer to the English language, and would not be understood as such without clarification. A logophile loves words, but this term does not specify which language and refers only to words, not language in the broad sense. You can just say "I love the English language". Descriptions such as fanatic and its synonyms may also be useful. For example, saying "I'm an English-language fanatic" would do a good job of expressing enthusiasm and eagerness to learn.
Yes, there is--sort of. The word is Anglophile, but it means a love of all things English, not just the English language. Your word would be understood (probably as synonymous with Anglophile), but it isn't the correct word. Nevertheless, you have used the suffix correctly in your invented word.
If you really wanted such a word, perhaps you could invent the word Anglo-linguaphile (googling it reveals no examples) and expect that it would be understood (by linguaphiles, at least) as one who loves the English language specfically.