It would violate the Lower House's own long-existing Rules on Proposing Amendments for the House of Representatives to propose amendments to the 1987 Constitution without the usual concurrence of the Senate, as in the case of enacting ordinary legislation.
Section 105. (House of Representatives) Form of Proposals and Procedure for Adoption. - Proposals to amend or revise the Constitution shall be by resolution which may be filed at any time by any Member. The adoption of resolutions proposing amendments to or revision of the Constitution shall follow the procedure for the enactment of bills.This means that the Lower House itself long ago decided against "voting jointly" and resolved any alleged ambiguity in the highly controverted provision in the 1987 Constitution that was used to try and force the establishment of a Unicameral Parliamentary system in 2007. --
Article XVII - Amendments Or Revisions - Section 1. Any amendment to, or revision of, this Constitution may be proposed by: (1) The Congress, upon a vote of three-fourths of all its Members; or (2) A constitutional convention.As far as the House is concerned therefore, the so-called Constituent Power granted to the Congress to propose amendments or revisions of the charter, shall be exercised in the same MODE as that of normal legislation (voting separately) but with the more stringent Three-fourths Majority Rule to approve proposed amendments being imposed by the Constitution itself. Of course, since they have the numbers, JDV and Co. could endeavour to change this Rule as they've been desperately trying to do the last few weeks in "marathon House sessions." Unfortunately for those in such a Big Rush, those existing Rules are also very specific about the manner of amending them -- tedious, time-consuming and self-enforcing.
ABSCBN News reports on the failure of JDV & Co. to change the Rules from "voting separately" to "voting jointly" using a beguiling set of "Proposed Rules for Constituent Assembly" which I found to be intentionally inscrutable on the matter of voting jointly or voting separately. Understandably. It also explains why, despite having the numbers, JDV & Co. have never dared to file a House Resolution proposing Amendments.
"Voting Jointly" has always been against the House's own Rules for proposing amendments to the Constitution.