1. ご苦労 gokuro
This is something that a boss says to their subordinates, please say お疲れ様です instead.
2. 一応 ichio／多分 tabun
You should avoid answering 一応／多分
meaning "Probably" to your boss when they ask you something.
The answer should be a yes or no.
3. 助かる tasukaru
You are not in the position to judge whether what your boss has done for you was thankful or not, by saying 助かりました meaning "That helped.".
A simple ありがとうございます would be much better.
4. わかりません wakarimasen
Even if you don't understand something, saying わかりません sounds like you don't care in the first place.
Tell your boss specifically what part you didn't understand, in order to sound more serious.
5. いいですか idesuka
If you want to get permission to do something, saying いいですか is a little too friendly.
"よろしいでしょうか" would be the right way to say it.
6. 了解 ryokai
The phrase has the nuance that you've approved what the person is saying, before confirming.
You have no right to judge if your boss's decisions are correct or not, so a "かしこまりました" would be better.
7. なるほど naruhodo
"なるほど" That makes sense sounds like you're evaluating what your bosses have said or taught you, or that you have the right to accept what you've been told or not.
Again, a "かしこまりました" would be more appropriate.
8. 頑張って ganbatte
Although you might have heard or used this phrase before, it should only be used among friends and family, or from a superior to a subordinate.
9. ごめんなさい gomennasai
Out of many ways to express your apologies in Japanese, ごめんなさい sounds like a child saying sorry to his/her parents when being scolded.
In a business situation, "申し訳ございません" would be the polite way to say it.
10. もちろん mochiron
Answering "もちろん" to your boss's question, makes them sound like they have asked you something really obvious.
This might make them feel very unplesant, so it's best to just answer with a simple "はい".
The three phrases that I recommend you to remember to have a decent relationship with your bosses and superiors are:
- はい hai
- かしこまりました kashikomarimashita
- ありがとうございます arigato-gozaimasu
This blog is recommended to those who are willing to study or work in Japan someday, and hopefully will be helpful when you interact with Japanese people.