### Describe the issue
When adding an individual observer through the "Add a new observer" form, the Phone Number field accepts alphabetic characters (a–z, A–Z). This indicates that validation is missing or inadequate.
### Steps to reproduce
Go to the Observers from the main menu
Click to Add individual observers from the Monitoring observers list
Fill "First name" from the "Add a new observer"
Fill "Last name" from the "Add a new observer"
Fill "Email" from the "Add a new observer"
Fill "Phone number" from the "Add a new observer"
_ ### Expected behavior_
- The "Phone number fields" should only accept numeric characters (0–9).
- Optionally, it may allow characters commonly used in phone numbers:
+(country code)
-(hyphen)
space
- Input containing alphabetic characters should be rejected with a clear validation message.
### Environment
Browser: Chrome 114
OS: EMUI 12.0.0
Device: Huawei Mate 10 Pro
### Additional context
### Describe the issue
When adding an individual observer through the "Add a new observer" form, the Phone Number field accepts alphabetic characters (a–z, A–Z). This indicates that validation is missing or inadequate.
### Steps to reproduce
Go to the Observers from the main menu
Click to Add individual observers from the Monitoring observers list
Fill "First name" from the "Add a new observer"
Fill "Last name" from the "Add a new observer"
Fill "Email" from the "Add a new observer"
Fill "Phone number" from the "Add a new observer"
_ ### Expected behavior_
### Environment
Browser: Chrome 114
OS: EMUI 12.0.0
Device: Huawei Mate 10 Pro
### Additional context