Source : https://consensys.net/knowledge-base/ethereum-2/faq/
Phase 0 has a soft target of end 2020.
Phase 0 will not do anything with regards to Ethereum network getting max utilized (currently at 95%) thanks to DeFi.
Phase 0 will not reduce gas fees and it will not reduce transaction confirmation time.
Ethereum will need Phase 1 & 2 for that (the shard chains), which is planned for later years.
In other words : if DeFi transactions keeps increasing on Ethereum network, it will get slower and slower and fees will get higher and higher.
This has happened once before with Ethereum, in 2018. Thanks to a certain Dapp called cryptokitties--> network congestion and high gas fees.
It has happened with Bitcoin too, during its bullrun in 2018 --> network congestion and high transaction fees.
Both networks are still missing transaction scalability.