Final answer:
The phrase 'when I was growing up' is an example of informal English, differing from the more formal language structure of the other options provided.
Step-by-step explanation:
The phrase from the excerpt that uses informal English is Option 4: 'when I was growing up'. This phrase tends to be conversational and casual, which is often seen in informal English. In contrast, the other options present more formal language typically used in written discourse. The discussion about the perception of English quality reflects on the broader societal attitudes towards what is considered 'proper' or 'standard' English. The stigma associated with different varieties of English can significantly impact people's self-esteem and social mobility, emphasizing that language is not just a tool for communication but also a key factor in expressing identity.