"Об" is followed by prepositional case, and according to this page, feminine nouns ending with "я" in prepositional should end with "е".
That said, it shouldn't be "об Англии" but rather "об Англие". What do I miss?
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The resource you were referring to oversimplified things too much. Words ending with "ь", "ия", "ие", "ий" end with "и" in prepositional, so "о речи", "о Франции", "о знамении" and "об аграрии".
I recommend you to refer to wiktionary whenever you have doubts - Russian section always comes with declensions, with "Англия" being no exception to that rule.