I
verb
BAD : She phoned to the hospital to ask about her husband.
GOOD : She phoned the hospital to ask about her husband.
BAD : Just phone to 555-879 and I'll come and get you.
GOOD : Just phone 555-879 and I'll come and get you.
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phone/telephone/ring/call a person/place/number (WITHOUT to ): 'You must promise to phone me as soon as you get there.'
Note that speakers of American English do not use ring for this meaning.
II
noun
BAD : I talked to him for a long time by phone last night.
GOOD : I talked to him for a long time on/over the phone last night.
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In British English the phrase is (talk/speak to sb) on/over the phone (NOT by phone ): 'He didn't want to discuss it over the phone.'
Note that in American English both by phone and on/over the phone are used, although by phone is not common.