The compound's name is silver(I) phosphide.
You can name this ionic compound by breaking it down into cation and anion.
Ionic compounds are always written using the cation first, followed by the anion. In your case, you're dealing with a silver cation and a phosphorus anion.
Now focus on finding their charges. For ionic compounds, the charge of the cation is written as the subscript of the anion and the charge of the anion is written as the subscript of the cation, without their respective signs.
Since the formula features silver with a subscript of
#"Ag"_3"P" -> 3"Ag"^(+) + "P"^(3-)#
For ionic compounds, roman numerals are used to express the oxidation state of the cation.
In your case, the silver cation is in a +1 oxidation state, which is another way of saying that it has a 1+ charge.
The phosphorus anion is called phosphide, which means that your ionic compound will be called silver(I) phosphide.
So remember, the cation comes first, the roman numeral comes second, and the anion comes last
#"silver "# #" "(I)"# #" ""phosphide"#