CREATE TABLE Phone
(
phoneID - PK
.
.
.
);

CREATE TABLE PhoneDetail
(
phoneDetailID - PK
phoneID - FK points to Phone
phoneTypeID ...
phoneNumber ...
.
.
.
);

CREATE TABLE Customer
(
customerID - PK
firstName
phoneID - Unique FK points to Phone
.
.
.
);

A customer can have multiple phone numbers e.g. Cell, Work, etc. phoneID in Customer table is unique and points to PhoneID in Phone table. If customer record is deleted, phoneID in Phone table should also be deleted.

Do you have any concerns on my design? Is this designed properly? My problem is phoneID in Customer table is a child and if child record is deleted then i can not delete the parent (Phone) record automatically.