How do you show the F1 phenotypes in a cross of parents heterozygous for both traits?

P  P  R  R
         p  Pp Pp Rp Rp
         p  Pp Pp Rp Rp
         r   Pr  Pr Rr  Rr  
         r   Pr  Pr Rr  Rr

ratio= 4:4:4:4
there it iss

For parents PPRR and pprr, all of the f1 will have the same genotype: PpRr. The PPRR can only give gametes of P and R, and the pprr can only give gametes with p and r. The only possible combination between gametes PR and pr is PpRr. You can diagram it - with only two options the punnett square does not look normal, but it would look like this:

___|_PR_
pr_|_PpRr

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Given the parents of PPRR and pprr, how do you show the possible F1 phenotypes in a cross of parents heterozygous for both traits.
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Here are a couple facts that follow necessarily from that ...

FACT 1. The offspring are PPRR and pprr
FACT 2. Heterozygous parents for both traits would be PpRr and PpRr.  So the parental cross is PpRr x PpRr

The first fact is completely superfluous: it can be deleted in full and not affect anything. That leaves us with ...

FACT. Heterozygous parents for both traits would be PpRr and PpRr.  So the parental cross is PpRr x PpRr

That already gives the genotypes of the parents.  The only thing left is to give is the phenotypes of the F1.  It is the usual 9:3:3:1 ratio for a dihybrid cross.  

9/16 of the offspring are expected to display dominant phenotypes for both characters

3/16 of the offspring are expected to display the dominant phenotype for the "P/p" character and the recessive phenotype for the "R/r" character

3/16 of the offspring are expected to display the recessive phenotype for the "P/p" character and the dominant phenotype for the "R/r" character

1/16 of the offspring are expected to display recessive phenotypes for both characters

I am sorry. your question doesn't quite make sense. are you looking for the F1 produced by crossing PRPR and prpr? in this case all offspring would be PpRr. However, if this is what you are looking for, then your statement that the parents are heterozygous is wrong. However if you are looking for a dihybrid cross of heterozygous parents for the alleles P and R then:

PpRr x PpRr

______PR______Pr______pR_____ _pr____
PR___PPRR____PPRr___PpRR___Pp Rr__
Pr____PPRr____PPrr____PpRr___ _Pprr___
pR___PpRR____PpRr____ppRR___p pRr___
pr____PpRr____Pprr_____ppRr__ __pprr___

genotype:
1 PPRR : 2 PPRr : 2 PpRR : 4 PpRr : 1 PPrr : 1 ppRR : 2 Pprr : 2 ppRr : 1 pprr
= 9 P_R_ : 3 P_rr : 3 ppR_ : 1 pprr