I only used that phrase to help those who seemed confused about it. It is the difference between knowing the way and following it. Between knowing Jesus Christ died on a cross and believing Jesus died on the cross for my sins. Nothing "modernist" about it and certainly not a false doctrine. In fact, it is those who doubt that we are justified by faith apart from works who insist on qualifiers for what saving faith really is. The idea of answering an altar call is mocked as something called "easy believism" - a term not found in Scripture. Whenever Jesus called for faith, to believe on Him, he did not have to expound on what that meant. When he said, "Whosoever believes in him has everlasting life.", he didn't follow up with instructions for all the additional things that have to be done to have eternal life.
Like Paul wrote in Romans 10:9-10
That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
I think the qualifiers come in with saving faith versus non-saving faith.
"Whosoever believes in him has everlasting life.", he didn't follow up with instructions for all the additional things that have to be done to have eternal life.
You might want to reconsider this opinion in light of what Jesus also taught about those who believe in Him.
Again, the error comes in when we try to separate faith and works, what we believe and how we act. It results in nonsense theology.
I’ve even seen some claim that repentance is a “work.”
Might as well go full Calvin.