fix: prompt phi (#1845) [skip ci]

* corecting phi system prompt

* phi test

* update

* add test

tests/test_prompters.py

@@ -42,6 +42,19 @@ class AlpacaPrompterTest(unittest.TestCase):
         assert "USER:" not in res
         assert "ASSISTANT:" not in res
 
+    def test_prompt_style_w_phi(self):
+        prompter = AlpacaPrompter(prompt_style=PromptStyle.PHI.value)
+        res = next(prompter.build_prompt("tell me a joke about the following"))
+        assert (
+            """<|system|>
+Below is an instruction that describes a task. Write a response that appropriately completes the request.<|end|>
+<|user|>
+tell me a joke about the following<|end|>
+<|assistant|>
+"""
+            == res
+        )
+
     def test_prompt_style_w_chat(self):
         prompter = AlpacaPrompter(prompt_style=PromptStyle.CHAT.value)
         res = next(