To find the total storage of the mobile phone after buying the additional bytes, we need to add the existing storage to the additional storage.
The existing storage is: \[ 1.28 \times 10^{11} \text{ bytes} \]
The additional storage is: \[ 384,000,000,000 \text{ bytes} = 3.84 \times 10^{11} \text{ bytes} \]
Now, we add the two amounts together:
\[ 1.28 \times 10^{11} + 3.84 \times 10^{11} \]
Since both quantities are in terms of \( 10^{11} \), we can combine them:
\[ (1.28 + 3.84) \times 10^{11} = 5.12 \times 10^{11} \text{ bytes} \]
Thus, the total storage of the phone, after purchasing the additional bytes, would be:
\[ \boxed{5.12 \times 10^{11}} \]