What also refers to is dependent on context. My phone is also ringing could mean at least any of the following:
- My phone is ringing in addition to my phone doing something else.
e.g. My phone is vibrating. My phone is also ringing.
- My phone is ringing in addition to someone else's phone ringing.
e.g. My sister's phone is ringing. My phone is also ringing.
- My phone is ringing in addition to some other person or thing ringing.
e.g. The church bells are ringing. My phone is also ringing.
Without context, the statement is ambiguous.
Changing the word order can help. My phone also is ringing is quite unnatural as a standalone sentence, but if the context is that another phone is ringing, you might say it that way to draw the parallel between your phone and the other phone. If you move also to the beginning or end of the sentence, and especially if you set it apart with a comma, then meaning #3 or the idea that the phone ringing coincides with some other activity is more strongly indicated (e.g. The market is crashing and the city is burning. Also, my phone is ringing). These are not foolproof, however, as context will still override.
- [I am selling meat.] I am also eating meat.
- [The cat is eating meat.] I am also eating meat.
- [I am eating eggs.] I am also eating meat.