Who are conditionally exempt from the payment of Final Capital Gains Tax?

Natural persons who dispose their principal residence, provided that the following criteria are met:

• The proceeds of the sale of the principal residence have been fully utilized in acquiring or constructing new principal residence within eighteen (18) calendar months from the date of sale or disposition;
• The historical cost or adjusted basis of the real property sold or disposed will be carried over to the new principal residence built or acquired;
• The Commissioner has been duly notified, through a prescribed return, within thirty (30) days from the date of sale or disposition of the person's intention to avail of the tax exemption;
• Exemption was availed only once every ten (10) years; and
• There is no full utilization of the proceeds of sale or disposition. The portion of the gain presumed to have been realized from the sale or disposition will be subject to Capital Gains Tax.
• In case of sale/transfer of principal residence, the Buyer/Transferee shall withhold from the seller and shall deduct from the agreed selling price/consideration the 6% capital gains tax which shall be deposited in cash or manager's check in interest-bearing account with an Authorized Agent Bank (AAB) under an Escrow Agreement between the concerned Revenue District Officer, the Seller and the Transferee, and the AAB to the effect that the amount so deposited, including its interest yield, shall only be released to such Transferor upon certification by the said RDO that the proceeds of the sale/disposition thereof has, in fact, been utilized in the acquisition or construction of the Seller/Transferor's new principal residence within eighteen (18) calendar months from date of the said sale or disposition. The date of sale or disposition of a property refers to the date of notarization of the document evidencing the transfer of said property. In general, the term "Escrow" means a scroll, writing or deed, delivered by the grantor, promisor or obligor into the hands of a third person, to be held by the latter until the happening of a contingency or performance of a condition, and then by him delivered to the grantee, promise or obligee.
  
  
  (Source: http://www.bir.gov.ph/taxinfo/tax_capgin.htm)