Please dont overthink amounts of individual nutrients. Calcium:phosphorous ratio is not something we use as it hugely complicates things, doesn’t take the diet as a whole into account and also there are local considerations such as the hardness of water.
The four safe veg that you can feed every day are lettuce, cucumber, bell pepper and coriander (cilantro).
There four veggies meet the nutritional needs of vitamins without being too high in calcium/oxalates.
Anything else can be added in rotation at once or twice a week.
High calcium veggies can be given in a small amount and at just once a week - things such as parsley, kale, spinach etc.
Fruit and carrot should not be fed, but if it is then it is only very small amount and no more often than once a week. The sugars in them are not healthy and fruits are not something they would naturally eat.
Most calcium comes into the diet via pellets and drinking water.
Pellets kept limited to one tablespoon and water should be filtered in hard water areas.
Mine get the basic four every single day but they do get another veg added in a couple of times a week but it depends what I have got in - I don’t buy specifically for them, I buy for us and our meal planning and they will then have a bit of it.
Mine, if they are incredibly lucky, might get a one small piece of carrot peeling at Christmas or a slice of apple once in the summer - I didn’t do it this year.
I don’t feed any pellets so I can feed the high calcium veggies such as kale and spinach without concern about overdoing the calcium.
Our guide explains everything fully
Long Term Balanced General And Special Needs Guinea Pig Diets
