Can I use these interchangeably?
I tried calling you, but you didn't answer the phone.
I tried calling you, but you wouldn't answer the phone

Question

Can I use these interchangeably?
I tried calling you, but you didn't answer the phone.
 I tried calling you, but you wouldn't answer the phone

Answer

Not quite.

The second one makes it sound like the person receiving the phone call might have been ignoring it on purpose. In other words, they could have answered the phone, but decided not to.

Answer

Not really. The second one implies an intentionality that isn't present in the first one.

I tried calling you, but you *didn't* answer the phone. - Just factual information. The person may not have heard it ring, or he couldn't answer at the time, or he intentionally ignored it.
I tried calling you, but you *wouldn't* answer the phone - Implies willful intention/decision *not* to answer the phone.

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