Hundreds of volunteers took part including children from local schools and colleges.
Mr Phillips added: "With over 90 organisations taking part, this has been Wales' largest river clean to date and we aim to continue to improve the environment in Wales with further community projects.
"We have a community of companies helping here and we have community of volunteers including schools and colleges, there's been lots and lots of support."
Volunteers from Keep Wales Tidy were involved in this year's clean-up as well as the one in August 2023 – when they also recovered three to four tonnes of scrap, 100 bags of litter, about 100 shopping trolleys, a fridge and traffic cones.
Owen Derbyshire, Keep Wales Tidy's chief executive officer, said: "It's a huge challenge but we know the health of our rivers is massively important not just at a community level but also at a national level.
"Times are tough at the moment, there isn't as much money in public finances but this is why it's more important than ever that we take individual responsibility."
He added that shopping trolleys were not ending up in the river by accident and "we need to call it out".
"We need to do all we can as a nation to reduce the amount of waste and that type of behaviour for the long term," he said.
Gerwyn Chillcot from Bridgend is volunteering at the clean-up and said the mess was "disgusting".
"To think all this mess that has been dumped over the years is disgusting, but it's good it's being cleaned up now for the environment.
"This is toxic at the end of the day and all the chemicals from the tyres are going into the water."
Sandra Ricardo from Cardiff Rivers group said it was unclear how the tyres ended up in the river.
Ms Ricardo said one theory is the tyres were used to "shore up" the edging of the river bank decades ago but also fears many could have been fly-tipped over the years.
"Why do people do this? You can take your rubbish to the council tip.
"Fly-tipping is a big issue especially in Cardiff. You see mattresses dumped and fridge freezers, it's a real problem."
Environmental campaigners said the toxic rubbish could wipe out the wildlife on the river.
Andrew Stride, from Ogmore Angling Association, said he had seen fish levels decrease in the river over the years,
"It has a huge impact on the fish population, these tyres are releasing chemicals that will affect the invertebrates and if they're killed off that will affect the fish and especially the salmon and sewin which come up this river.
"This toxic waste will just make it even worse."
Angharad Brown, president of the Merthyr Mawr Women's Institute, co-ordinated volunteers at the clean-up operation.
"It's important for us to be involved in such a worthwhile community project, which fits in with our own campaign for cleaner rivers and waterways in Wales," she said.
