From my understanding you have a form that needs to be filled but this form has both details of PERSON table and also the PHONE table.

Now, you want to know how to insert these details into the respective tables?

If the above scenarios are true, then, since you designed the form - you obviously have variables to accept the user inputs say $fn for First_Name something like that??

From your post these will be your tables:
person> pID (not null, auto_increment), lastname, firstname
phone>pID (not null), phoneNum, pID(foreign key points to "person")

PHP Syntax (Toggle Plain Text)

sql='insert into person (pid, lastname, firstname) values ("NULL", "$ln","$fn")';

sql='insert into person (pid, lastname, firstname) values ("NULL", "$ln","$fn")';

you can use a variable to accept the last pid from MySQL and use that variable as input to the second table ie. supposing you use $ppid

PHP Syntax (Toggle Plain Text)

$sql2='insert into phone (pid, phoneNum) values ("$ppid", "$phno")';

$sql2='insert into phone (pid, phoneNum) values ("$ppid", "$phno")';