Here are some professional and empathetic phrases to apologize to a customer:

1. **General Apology** 
   - "We sincerely apologize for the inconvenience caused."  
   - "I’m sorry to hear about this situation, and I want to help resolve it for you."  
   - "Please accept our apologies for any frustration this has caused."  

2. **For Delays**:  
   - "We’re sorry for the delay and truly appreciate your patience."  
   - "I apologize for the extended wait time; we’re working to resolve this as quickly as possible."  

3. **For Mistakes**:  
   - "We deeply regret the error and are taking steps to ensure it doesn’t happen again."  
   - "I’m sorry for the mistake; we value your trust and are committed to making this right."  

4. **For Poor Service**:  
   - "I’m sorry we didn’t meet your expectations; let us make it up to you."  
   - "We apologize for not providing the service you deserve and will address this promptly."  

5. **Reassurance**:  
   - "We take full responsibility for this and are already working on a solution."  
   - "Your satisfaction is important to us, and we’ll do whatever we can to resolve this issue."