I have a few questions and a few suggestions also.
Improving Written English
What about the standard of your written English? If you are satisfied that you can write without errors in grammar and have an adequate vocabulary, then the problem should be addressed differently.
Challenges with Oral Communication
Problems only with oral communication mean a lack of practice (or opportunity) when you learned the language and fear when you actually use it, particularly in the office and in front of the boss.
The fear and hesitation should be handled by building up confidence, and I have seen great results in the use of NLP for this purpose.
But still, you cannot, in conversation, take time to compose a grammatically correct sentence and rehearse it before you deliver it. Our speaking should almost be spontaneous—perhaps we think and speak simultaneously.
For this purpose, you may read "conversation-oriented texts"—these are comics. Writers of comics use very simple sentences, generally the way children speak. Read them repeatedly (with good attention, of course), and you will soon become familiar with the structure of communicative forms of English.
There are about 50 to 100 sentence patterns generally required for office conversations—we only change the subject, verb, objects, etc., in these sentence structures.
Repeated reading of such sentences in comic books will help you start using correct grammar without being conscious of it. You will only notice if the grammar is incorrect in a sentence. When you read a sentence with correct grammar, you will not notice it; you will only pick up the meaning of the sentence and move to the next one quickly.
Once you can spontaneously form a sentence that is grammatically correct, you can focus on the content of what you communicate rather than the syntax.
(At present, as you strain to get the syntax correct, you may lose focus on the content. This means disaster and loss of confidence, etc., etc.)
Late "Uncle Pai," the journalist who created comics and children's books (Amar Chitra Katha, for example), rendered a great service to present-age Indian school children. He made them read English with interest and talk with confidence.
This method will work very well with children, but I am sure grown-ups will also benefit with requisite practice.
Listening to conversations, talk shows, drama, etc., will also help in "spontaneous sentence framing."
Only after we achieve this "spontaneous sentence framing" will our vocabulary, pronunciation, punctuation, etc., help.
With best wishes.
Regards, Srinivasan