I haven't seen teh connection between high phosphate and nuisance algae as has often been pointed out. Before I stumbled across the research done by ROhwer and others showing the antagonistc relationship between algae and corals it seemed obvious to me having tanks with "high" phospphate and not nuisance algae issues there was something a lot more complex happening.
Richard Ross's video by BRS does a good job discussing this.
As far as size of the water change controlled studies I'm pretty sure would show an optimum percentage and frequency. I've settled on relatively small weekly or biweekly because in my experiences in dealling with these issues over the years larger ones, in the range of 30% to 50%, were a lot of work and didn't seem to me to be any more productive or quicker in reducing algae growth from week to week. I want to emphasize I do not have a magic number to use. Each system and each problem will have their differences. WHat I have seen is I would say seems a rough correltation to the general cycles given by Nilsen and Fossa in their books "The Mordern Coral Reef Aquarium".
One of my more educational expericenes was maintianing a reef system in a house that was unoccupied for 3 years. There were three separate occasions the system was crashed due to realitors or electricians leaving doors open or turning off power. Each time there were fish and corals that survived. Each time the owner choose not to put any effort in remediation, just continue basic weekly maintnenace which included 5%-8% water changes. Each time the system corrected it self and nuisance algae dissappeared over roughly 6-8 months. This was without the scrubbing or aggressive siphoning I did in the above links. This was a revelation to me nuisance algae could be corrected just with small weekly water changes.
Now, getting into the problems of reducing PO4 is another very complicated subject. Here's links if you want to dig into the research here's some links:
https://www.cambridge.org/core/jour...reef-corals/AFB1CF4CB68823BD13AD254623FD3C7C#
An Experimental Mesocosm for Longterm Studies of Reef Corals
Phosphate Deficiency:
Nutrient enrichment can increase the susceptibility of reef corals to bleaching:
https://www.nature.com/articles/nclimate1661
Ultrastructural Biomarkers in Symbiotic Algae Reflect the Availability of Dissolved Inorganic Nutrients and Particulate Food to the Reef Coral Holobiont:
https://www.frontiersin.org/articles/10.3389/fmars.2015.00103/full
Phosphate deficiency promotes coral bleaching and is reflected by the ultrastructure of symbiotic dinoflagellates
https://www.sciencedirect.com/science/article/pii/S0025326X17301601?via=ihub
Effects of phosphate on growth and skeletal density in the scleractinian coral Acropora muricata: A controlled experimental approach
https://www.sciencedirect.com/science/article/pii/S0022098111004588
High phosphate uptake requirements of the scleractinian coral Stylophora pistillata
http://jeb.biologists.org/content/214/16/2749.full
Phosphorus metabolism of reef organisms with algal symbionts
https://esajournals.onlinelibrary.w...98e60zfBEvx5IcIVGhmlpUYmzIJuqUNVm0sG8_0vth6lq
https://therichross.com/skeptical-reefkeeping-ix-test-kits-chasing-numbers-and-phosphate/
Sponge symbionts and the marine P cycle
https://www.pnas.org/content/112/14/4191
Phosphorus sequestration in the form of polyphosphate by microbial symbionts in marine sponges
https://www.pnas.org/content/112/14/4381