How to replace a word in a text and store the found word in a database table in php?

[Tosey]

$text = "i am a student of oxford university, and i love to tell everyone how much i have enjoyed my four years in school. the whole environment was really welcoming" .

Actually, we have a database table called "text_word". So, i want a script that will search through the above text and check if any of those words from the above text does not exist in the "text_word" table, such word should be replaced by asterisks and store the replaced word into a separate column called "unmatched_word" in the same "text_word" table.

let's assume the word "welcoming" was not existing in my database what i want to achieve is this. the text is parsed through the program

INPUT:  "i am a student of oxford university, and i love to tell everyone how much i have enjoyed my four years in school. the whole environment was really welcoming" .

OUTPUT: "i am a student of oxford university, and i love to tell everyone how much i have enjoyed my four years in school. the whole environment was really ******" .

Code Sample:
foreach ($text as $word) {
        
     $select_word = $f->filterRecord("*", "parts_of_speech", "word", $word);
     $get_word = $f->show_data($select_word);
     $count_words = $f->numR($select_word);
        
     if ($count_words > 0) {
         $result[] = '<a href="word/?w='.$word.'">'.$word.'</a>';
     } else {
         $result[] = "******";
     }
        
    }

Please i believe the code is not doing exactly what i want. If you have a better approach to how i can get the job done, i don't mind if you give me a fresh code snippet or script. I hope you understand what i'm trying to do now?

[justsomeguy]

That code is using several methods that you didn't show the code for, but why don't you think it's doing what you want?  What is it doing instead?