Sweet potato leaves are the natural leaves of sweet potatoes.
We’ve already looked at sweet potatoes, but what of their leaves. Can guinea pigs eat them?
Calories 35.0(147 kJ) 2%

Total Carbohydrate 6.4g 2%
Dietary Fiber 2.0g8%
Fats & Fatty Acids
Amounts Per Selected Serving%DV
Total Fat 0.3g 0%
Saturated Fat 0.1g 0%
Monounsaturated Fat 0.0g
Polyunsaturated Fat 0.1g
Protein 4.0g 8%
Vitamin A 1028IU 21%
Vitamin C 11.0mg 18%
Thiamin 0.2mg 10%
Riboflavin 0.3mg 20%
Niacin 1.1mg 6%
Vitamin B 60.2mg 9%
Folate 80.0mcg 20%
Vitamin B 120.0mcg 0%
Pantothenic Acid 0.2mg 2%
Calcium 37.0mg 4%
Iron 1.0mg 6%
Magnesium 61.0mg 15%
Phosphorus 94.0mg 9%
Potassium5 18mg 15%
Sodium9.0mg0%
Zinc 0.3mg 2%
Copper 0.0mg 2%
Manganese 0.3mg 13%
Selenium 0.9mcg 1%
Read More http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2664/2#ixzz2spSnosRQ
As you can see they do contain little phosphorus, a hint of calcium and fat, and are quite acidic.
With that in mind, guinea pigs can eat sweet potato leaves but only one to two times a week due to their acidic and phosphorus content.