Some babies make it and some don't. It is very difficult to know why. I have a baby who was 40 grams at birth, hand-fed for 3 weeks. He grew up into a beautiful show pig. Another baby was 49 grams at birth, I held her 24/7 and hand-fed her every 1.5 hours. She developed some complications. She passed in my hands on the 14th day. Usually, if they are not going to make it, they pass away on the 5th day or sooner. Raising guinea pigs can be joyful. But for every live baby, there is another who died and it breaks your heart. I'm sure Phoenix was loved in the precious short time you nursed him as a baby. He is in a better place now. So, try to be cheerful for him.